scholarly journals Study on vibration characteristics of damping blade with snubber and shroud based on fractal theory

2016 ◽  
Vol 20 (suppl. 3) ◽  
pp. 887-894 ◽  
Author(s):  
Wei Zhao ◽  
Liang-Liang Li ◽  
Di Zhang
Keyword(s):  
Nonlinear Vibration ◽  
Steam Turbine ◽  
Fractal Geometry ◽  
Fractal Theory ◽  
Damping Ratio ◽  
Friction Model ◽  
Contact Forces ◽  
Normal Contact ◽  
Resonant Amplitude ◽  
Last Stage

Snubber and shroud have been widely adopted in steam turbine last stage blades to decrease the vibration stress. The contact surfaces between snubber and shroud own obviously fractal geometry characteristics. Based on fractal geometry theory and finite element nonlinear vibration theory, the fractal friction model that describes friction damping contact could be accurately established. In this paper, the contact fractal elements are set up and the nonlinear vibration response characteristics of a long steam turbine last stage blade with snubber and shroud are calculated. The results show that, with the increase of shroud normal force, the resonant amplitude of the blade experiences a decreasing period followed by an increasing period while the modal damping ratio increases first and then decreases when there is only shroud contact. The regulations are similar when there are both shroud and snubber contacts. The resonant frequency increases until the normal contact forces increase to some degree.

Analysis of Vibration Characteristics for Last Stage Blade With Friction Contact Surfaces of Steam Turbine

2011 ◽  
Author(s):  
Yutaka Yamashita ◽  
Koki Shiohata ◽  
Takeshi Kudo
Keyword(s):  
Dynamic Response ◽  
Steam Turbine ◽  
Contact Surface ◽  
Contact Forces ◽  
Analysis Method ◽  
Friction Damping ◽  
Normal Contact ◽  
Damping Characteristics ◽  
Last Stage ◽  
Contact Surfaces

Friction damping devices such as under platform dampers are installed for modern turbine blades to suppress dynamic vibrations of the blades. In order to secure the reliability of the blades, it is important to predict the dynamic response and friction damping characteristics accurately. In this present paper, the dynamic response and friction damping characteristics of a last stage blade (LSB) of a steam turbine with contact surfaces at the cover, tie-boss and blade root was investigated. Especially, it is focused on the effect of the non-uniform normal contact forces at the contact surface. To investigate the effect of non-uniform normal contact forces, an analysis method was developed. Analysis model of the LSB with contact surfaces was discretized by finite elements. Tangential forces at the contact surfaces were modeled by multi-DOF macro-slip modeling. The non-linear frequency responses of the LSB were obtained by using the harmonic balance method. Using this analysis method, the relationship between the contact surface behavior and the dynamic response was studied.

Experimental Friction Damping Characteristic of a Steam Turbine Blade Coupled by Shroud and Snubber at Standstill Set-Up

2012 ◽  
Author(s):  
Jun Wu ◽  
Yonghui Xie ◽  
Di Zhang ◽  
Minghui Zhang
Keyword(s):  
Steam Turbine ◽  
Turbine Blade ◽  
Rotational Speed ◽  
Damping Ratio ◽  
Turbine Blades ◽  
Contact Forces ◽  
Normal Contact ◽  
Modal Damping Ratio ◽  
Modal Damping ◽  
Steam Turbine Blade

In order to avoid the high cycle fatigue which leads to the failure of turbine blades, friction structural damping has been widely used in turbine blade designs to reduce vibratory stresses by energy dissipation. A method is developed here to analyze the influence of friction structural damping on the vibration characteristics of turbine blades. Vibratory responses of a long steam turbine blade with shroud and snubber are studied. Finite element contact analysis of the steam turbine blades which are modeled in 3-D solid elements is conducted to obtain the normal contact force on the shroud contact surface and snubber contact surface of adjacent blades under five different rotational speeds (2100rpm, 2200rpm, 2413rpm, 2600rpm and 3000rpm). A rig for the tests of non-rotating turbine blade with friction damping structure is built. The normal contact forces of the shroud and snubber are applied to the blade according to numerical results. The response curves and modal damping ratios of the blade under different normal contact forces, which each one is related to a different rotational speed, are obtained. The experimental results show that with increases in rotational speed, modal damping ratio of the blade experiences an increasing period followed by a decreasing period while the resonance amplitude decreases first and then increases when there is only shroud contact. The effects are similar when there are both shroud and snubber contact. The modal damping ratio of the blade is basically identical with that of the uncoupled blade for the rotational speed above 2600rpm. For this range of rotational speed, the resonance frequency increases with the increase of rotational speed, and the changes of the resonance frequency are very trivial.

A Fractal Contact Friction Model and Nonlinear Vibration Response Studies of Loosely Assembled Blade With Dovetail Root

2016 ◽  
Author(s):  
Shangguan Bo ◽  
Yu Feilong ◽  
Duan Jingyao ◽  
Gao Song ◽  
Xiao Junfeng ◽  
...  
Keyword(s):  
Nonlinear Vibration ◽  
Fractal Geometry ◽  
Friction Model ◽  
Structure Design ◽  
Forced Response ◽  
Vibration Response ◽  
Contact Friction ◽  
Friction Contact ◽  
Stick Slip ◽  
Proposed Model

To investigate the friction damping effect of a loosely assembled blade with dovetail root, a fractal contact friction model is proposed to describe the friction force. In the proposed model, the friction contact interface is discretized to a series of friction contact pairs and each of them can experience stick, slip, or separate. Fractal geometry is used to simulate the topography of contact surfaces. The contact stiffness, which is related to the parameters of contact interfaces including normal load, roughness, Young’s modulus, and Poisson’s ratio, is calculated using Hertz contact theory and fractal geometry. The nonlinear vibration response of loosely assembled blade with dovetail root is predicted using the proposed model, the multiharmonic balance method and Newton iterative algorithm. The effect of centrifugal force, friction coefficient and exciting force on the forced response of a loosely assembled blade with dovetail root is studied. The numerical vibration responses are compared to the experimental results. It will verify the reliability of the numerical method and provide theoretical basis for structure design of the loosely assembled blade with dovetail root.

Modeling and simulation of dynamics of a planar-motion rigid body with friction and surface contact

2017 ◽  
Vol 31 (16-19) ◽  
pp. 1744021 ◽  
Author(s):  
Xiaojun Wang ◽  
Jing Lv
Keyword(s):  
Rigid Body ◽  
Frictional Contact ◽  
Lagrange Equation ◽  
Linear Complementarity ◽  
Friction Model ◽  
Contact Forces ◽  
Planar Motion ◽  
Stick Slip ◽  
Normal Contact ◽  
Friction Law

The modeling and numerical method for the dynamics of a planar-motion rigid body with frictional contact between plane surfaces were presented based on the theory of contact mechanics and the algorithm of linear complementarity problem (LCP). The Coulomb’s dry friction model is adopted as the friction law, and the normal contact forces are expressed as functions of the local deformations and their speeds in contact bodies. The dynamic equations of the rigid body are obtained by the Lagrange equation. The transition problem of stick-slip motions between contact surfaces is formulated and solved as LCP through establishing the complementary conditions of the friction law. Finally, a numerical example is presented as an example to show the application.

Improved Dynamic Friction Models for Simulation of One-Dimensional and Two-Dimensional Stick-Slip Motion

2000 ◽  
Vol 123 (4) ◽  
pp. 661-669 ◽  
Author(s):  
Fitsum A. Tariku ◽  
Robert J. Rogers
Keyword(s):  
Mechanical Systems ◽  
Friction Model ◽  
Contact Forces ◽  
Force Balance ◽  
Two Dimensional ◽  
Lumped Mass ◽  
Stick Slip ◽  
Normal Contact ◽  
One Dimensional ◽  
Friction Models

In many mechanical systems, the tendency of sliding components to intermittently stick and slip leads to undesirable performance, vibration, and control behaviors. Computer simulations of mechanical systems with friction are difficult because of the strongly nonlinear behavior of the friction force near zero sliding velocity. In this paper, two improved friction models are proposed. One model is based on the force-balance method and the other model uses a spring-damper during sticking. The models are tested on hundreds of lumped mass-spring-damper systems with time-varying excitation and normal contact forces for both one-dimensional and two-dimensional stick-slip motions on a planar surface. Piece-wise continuous analytical solutions are compared with solutions using other published force-balance and spring-damper friction models. A method has been developed to set the size of the velocity window for Karnopp’s friction model. The extensive test results show that the new force-balance algorithm gives much lower sticking velocity errors compared to the original method and that the new spring-damper algorithm exhibits no spikes at the beginning of sticking. Weibull distributions of the sticking velocity errors enable maximum errors to be estimated a priori.

scholarly journals Failure Analysis in Lacing Wire Of Last Stage Low Pressure Steam Turbine Blade

2021 ◽  
Vol 1096 (1) ◽  
pp. 012097
Author(s):  
A M Kongkong ◽  
H Setiawan ◽  
J Miftahul ◽  
A R Laksana ◽  
I Djunaedi ◽  
...  
Keyword(s):  
Failure Analysis ◽  
Steam Turbine ◽  
Turbine Blade ◽  
Low Pressure ◽  
Pressure Steam ◽  
Steam Turbine Blade ◽  
Last Stage

A Nonlinear Rail Vehicle Dynamics Computer Program SAMS/Rail: Part 1—Theory and Formulations

2009 ◽  
Author(s):  
Khaled E. Zaazaa ◽  
Brian Whitten ◽  
Brian Marquis ◽  
Erik Curtis ◽  
Magdy El-Sibaie ◽  
...  
Keyword(s):  
High Speed ◽  
Dynamic Performance ◽  
Three Dimensional ◽  
Contact Element ◽  
Contact Forces ◽  
Simulation Code ◽  
Vehicle Performance ◽  
Normal Contact ◽  
Advantages And Disadvantages ◽  
High Speed Trains

Accurate prediction of railroad vehicle performance requires detailed formulations of wheel-rail contact models. In the past, most dynamic simulation tools used an offline wheel-rail contact element based on look-up tables that are used by the main simulation solver. Nowadays, the use of an online nonlinear three-dimensional wheel-rail contact element is necessary in order to accurately predict the dynamic performance of high speed trains. Recently, the Federal Railroad Administration, Office of Research and Development has sponsored a project to develop a general multibody simulation code that uses an online nonlinear three-dimensional wheel-rail contact element to predict the contact forces between wheel and rail. In this paper, several nonlinear wheel-rail contact formulations are presented, each using the online three-dimensional approach. The methods presented are divided into two contact approaches. In the first Constraint Approach, the wheel is assumed to remain in contact with the rail. In this approach, the normal contact forces are determined by using the technique of Lagrange multipliers. In the second Elastic Approach, wheel/rail separation and penetration are allowed, and the normal contact forces are determined by using Hertz’s Theory. The advantages and disadvantages of each method are presented in this paper. In addition, this paper discusses future developments and improvements for the multibody system code. Some of these improvements are currently being implemented by the University of Illinois at Chicago (UIC). In the accompanying “Part 2” and “Part 3” to this paper, numerical examples are presented in order to demonstrate the results obtained from this research.

Some Experiments on Wet Steam Flow Visualization in Large Steam Turbine Blading

1976 ◽  
Vol 98 (3) ◽  
pp. 573-577 ◽  
Author(s):  
J. Krzyz˙anowski ◽  
B. Weigle
Keyword(s):  
Steam Turbine ◽  
Steam Flow ◽  
Light Sources ◽  
Phase Flow ◽  
Wet Steam ◽  
Experimental Conditions ◽  
Advantages And Disadvantages ◽  
Primary Droplet ◽  
Last Stage ◽  
Wet Steam Flow

In a series of experiments aimed at the visualization of the wet steam flow in the exhaust part of a 200 MW condensing steam turbine a set of periscopes and light sources was used. The aim of the experiment was: 1 – The investigation of the liquid-phase flow over the last stage stator blading of the turbine mentioned. 2 – The investigation of the gaseous-phase flow through the last stage blading at full and part load. The first part of the program partially failed due to the opaqueness of the wet steam atmosphere for the turbine load higher than 10–20 MW. The detailed experimental conditions will be described. An assessment of the primary droplet size will also be given. The preliminary results of the second part of the program will be outlined. The advantages and disadvantages of the equipment used will be discussed.

Modeling of a Steam Turbine Including Partial Arc Admission for Use in a Process Simulation Software Environment

2011 ◽  
Author(s):  
Eric Liese
Keyword(s):  
Steam Turbine ◽  
Process Simulation ◽  
Process Model ◽  
Constant Pressure ◽  
Pressure Ratio ◽  
Simulation Software ◽  
State Variables ◽  
Steam Turbines ◽  
Software Environment ◽  
Last Stage

A dynamic process model of a steam turbine, including partial arc admission operation, is presented. Models were made for the first stage and last stage, with the middle stages presently assumed to have a constant pressure ratio and efficiency. A condenser model is also presented. The paper discusses the function and importance of the steam turbines entrance design and the first stage. The results for steam turbines with a partial arc entrance are shown, and compare well with experimental data available in the literature, in particular, the “valve loop” behavior as the steam flow rate is reduced. This is important to model correctly since it significantly influences the downstream state variables of the steam, and thus the characteristic of the entire steam turbine, e.g., state conditions at extractions, overall turbine flow, and condenser behavior. The importance of the last stage (the stage just upstream of the condenser) in determining the overall flowrate and exhaust conditions to the condenser is described and shown via results.

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