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.

Evaluation of Friction Damping in Dovetail Root Joints Based on Dissipation Energy on Contact Surfaces

2009 ◽  
Author(s):  
Kunio Asai ◽  
Shigeo Sakurai ◽  
Takeshi Kudo ◽  
Norihiko Ozawa ◽  
Taizo Ikeda
Keyword(s):  
Contact Force ◽  
Contact Stiffness ◽  
Relative Displacement ◽  
Contact Angles ◽  
Forced Response ◽  
Contact Forces ◽  
Friction Damping ◽  
Normal Contact ◽  
Tangential Contact ◽  
Contact Surfaces

It is necessary to increase and estimate friction damping at contact interfaces to reduce vibratory stresses in turbines. The hysteresis behavior between tangential contact force and relative displacement should be precisely estimated to improve the accuracy of fiction-damping estimates. There is a difficulty in establishing a general model of hysteresis because tangential contact stiffness depends on many parameters, such as normal contact force, contact geometry, surface roughness, and wear status. We discuss a procedure to empirically calculate friction damping in dovetail root joints using the tangential contact stiffness estimated from measured natural frequencies and the micro-slip model whose coefficients were experimentally obtained from special fretting tests. Instead of the multi-harmonic balance methods, we calculated the friction damping on the basis of the energy dissipation at contact surfaces to discuss the effects of the tangential contact stiffness on several physical values, i.e., tangential and normal contact forces, natural frequency, and micro-slip. In our model, the linear forced response analysis was conducted by taking into consideration the non-linearity between the tangential contact force and the relative displacement by defining the actual and imaginary tangential contact stiffness. We confirmed that the numerically calculated damping ratios are quantitatively in very good agreement with the measured ones under different contact angles, input gravity levels, and contact forces. This indicates that if the tangential contact stiffness is accurately estimated, friction damping with our method can be precisely estimated under different test conditions. We also showed that the estimated tangential contact stiffness for dovetail root joints are smaller than those obtained by the fretting tests at high input gravity. This is probably because the contact interface partially separates during a cyclic loading in the former case; this results in the decrease of the contact area and contact stiffness.

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.

Friction Damping of Interlocked Vane Segments: Experimental Results

2001 ◽  
Author(s):  
T. Berruti ◽  
S. Filippi ◽  
M. M. Gola ◽  
S. Salvano
Keyword(s):  
Numerical Analysis ◽  
Energy Dissipation ◽  
Contact Surface ◽  
Aircraft Engine ◽  
Experimental Methods ◽  
Experimental Results ◽  
Contact Model ◽  
Friction Damping ◽  
Contact Surfaces ◽  
Adjacent Segments

Experimental methods and results of the stator bladed segment of an aircraft engine are presented. Investigation concern the energy dissipation due to friction between contact surfaces of adjacent segments. The influence of the force normal to the contact surface (due to interference between adjacent segments) on friction damping is shown. Moreover the experiments show the nature of friction at contact surfaces. The parameters of a contact model to be used in a numerical analysis have been identified from the experiments.

scholarly journals Effects of Object Compliance on Three-Digit Grasping

2009 ◽  
Vol 101 (5) ◽  
pp. 2447-2458 ◽  
Author(s):  
Sara A. Winges ◽  
Stephanie E. Eonta ◽  
John F. Soechting ◽  
Martha Flanders
Keyword(s):  
Contact Surface ◽  
Muscle Activation ◽  
Ring Finger ◽  
Contact Forces ◽  
Load Force ◽  
Electromyographic Activity ◽  
Dependent Manner ◽  
Muscle Activation Patterns ◽  
Contact Points ◽  
Contact Surfaces

Compared with rigid objects, grasping and lifting compliant objects presents additional uncertainties. For any static grasp, forces at the fingertips depend on factors including the locations of the contact points and the contact forces must be coordinated to maintain equilibrium. For compliant objects, the locations and orientations of the contact surfaces change in a force-dependent manner, thus changing the force requirements. Furthermore, every force adjustment then results in additional changes in object shape. This study characterized force and muscle activation patterns in this situation. Fingertip forces were measured as subjects grasped and lifted a 200-g object using their thumb, index, and ring fingers. A spring was sometimes placed under the index and/or ring finger contact surface. Surface electromyographic activity was recorded from ten hand muscles and one proximal arm muscle. The patterns of grip (normal) force and muscle activity were similar across conditions during the load and lift phases, but their amplitude depended on whether the contact surface was compliant. Specifically, the grip force increased smoothly during the load phase of the task under all conditions. To the contrary, the tangential contact (load) force did not increase monotonically when one or more of the contact surfaces were compliant, resulting in a decoupling of the grip and load forces.

Friction Damping of Interlocked Vane Segments: Experimental Results

2002 ◽  
Vol 124 (4) ◽  
pp. 1018-1024 ◽  
Author(s):  
T. Berruti ◽  
S. Filippi ◽  
M. M. Gola ◽  
S. Salvano
Keyword(s):  
Numerical Analysis ◽  
Energy Dissipation ◽  
Contact Surface ◽  
Aircraft Engine ◽  
Experimental Methods ◽  
Experimental Results ◽  
Contact Model ◽  
Friction Damping ◽  
Contact Surfaces ◽  
Adjacent Segments

Experimental methods and results of the stator bladed segment of an aircraft engine are presented. Investigation concerns the energy dissipation due to friction between contact surfaces of adjacent segments. The influence of the force normal to the contact surface (due to interference between adjacent segments) on friction damping is shown. Moreover, the experiments show the nature of friction at contact surfaces. The parameters of a contact model to be used in a numerical analysis have been identified from the experiments.

The Vibration Characteristics of Steam Turbine Blades with New Friction Damping Structures

2013 ◽  
Vol 312 ◽  
pp. 268-272
Author(s):  
Jun Wu ◽  
Rui Shan Yuan ◽  
Peng Fei Zhao ◽  
Yong Hui Xie
Keyword(s):  
Finite Element ◽  
Steam Turbine ◽  
Contact Surface ◽  
Turbine Blades ◽  
Harmonic Balance Method ◽  
Equivalent Stiffness ◽  
Friction Damping ◽  
Element Analysis ◽  
Steam Turbine Blades ◽  
Stiffness And Damping

The hysteresis curves that show the relationship between the tangential friction force and relative displacement of the contact surface were measured. The equivalent stiffness and damping of the friction contact surface under different normal loads were computed by harmonic balance method (HBM). The finite element model of steam turbine blades with new friction damping structures was established. The effects of friction between the contact surfaces were considered by using spring damping elements to connect the friction damper and the blade. The equivalent stiffness and damping which were calculated by the experiment results were applied to the spring damping elements under different rotational speeds. Based on the natural frequencies which were computed by finite element analysis, the Campbell diagram of the whole blades was obtained. The results showed that there were no 3-coincide points in the working speed range.

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.

The Influence of the Suspension on the Phenomena of Wheel-Rail Contact

2015 ◽  
Vol 809-810 ◽  
pp. 1061-1066
Author(s):  
Ioan Sebeşan ◽  
Valeriu Ştefan
Keyword(s):  
Contact Surface ◽  
Contact Problems ◽  
Contact Forces ◽  
Dynamic Loads ◽  
Friction Forces ◽  
Normal Contact ◽  
The Moment ◽  
The Relationship ◽  
Contact Pressures ◽  
Pivoting Friction

Efficient use of adhesion between wheels and rails involves a good knowledge of this phenomenon, in order to equip the vehicle with adequate facilities and systems that protect the vehicle and the rail. The loading of the vehicle's axle with dynamic loads in vertical and horizontal planes, are to be developed in the area of contact, both normal stress and shear distributed stress, their sum giving the friction force and the moment of pivoting friction (spin). This makes the wheel-rail contact problems take the two aspects of the study, namely the problem of normal and tangential contact issue. The normal contact problem involves regular geometric shape bodies, determining the size of the resulting contact surface, the distribution of the normal contact pressures and the relationship between the proximity of the bodies and the normal contact force. Solving the problem of the tangential wheel-rail contact is about to establish the correlation between the creepage, normal contact forces and friction forces, and also the ratio between the adherent contact surface and the nominal contact surface where the creepage ocurs.

Analysis and Verification Test of Damping Characteristics of Steam Turbine Hollow Vane With Friction Damper

2014 ◽  
Author(s):  
Yasutomo Kaneko ◽  
Hiroyuki Yamashita ◽  
Hiroharu Ooyama
Keyword(s):  
Steam Turbine ◽  
High Capacity ◽  
Analysis Method ◽  
Structural Damping ◽  
Friction Damper ◽  
Flat Plates ◽  
Aerodynamic Damping ◽  
Damping Characteristics ◽  
Excited Vibration ◽  
Turbine Vane

A vane used in a low pressure end of a steam turbine is usually fixed to a shroud and a casing by welding both ends. In such a vane structure, the damping in loading operation is comprised of the material damping and the aerodynamic damping, because the structural damping is very small. In the blade and vane of high-capacity steam turbine units, the aerodynamic damping may become negative under the high loading operation, and some papers reported the self-excited vibration of the blade and vane caused by the negative aerodynamic damping. Recently, in order to increase the reliability of the steam turbine vane, a hollow vane with a friction damper has been proposed. In such a steam turbine vane, the curved damper piece made of the thin plate is inserted into the hollow vane, and the structural damping is added by use of the friction between the damper piece and the vane. In this paper, for the purpose of clarifying the damping characteristics of the hollow vane with the friction damper, first, the excitation test of the model vane is carried out. In the excitation test of the model vane, the damping characteristics of the model vane consisting of two flat plates and the thin curved damper piece are measured, changing the excitation force. Second, the analysis method for predicting the damping characteristics of the hollow vane with the friction damper, which utilizes the conventional modal analysis method and the harmonic balance method, is proposed. The validity of the analysis method is verified by comparing the measured damping with the calculated ones. After verifying the analysis method, the actual steam turbine hollow vane with the friction damper is also analyzed, and the effect of the damper stiffness on the damping characteristics is examined. Finally, the actual hollow vane with the friction damper for the high-capacity steam turbine unit is designed and manufactured, and the excitation test of the actual hollow vane is carried out. From these results, the damping characteristics of the hollow vane with the friction damper are clarified.

Appreciable Increase in Pitting Limit of Contact Surfaces Under Rolling and Sliding Conditions

1978 ◽  
Vol 100 (3) ◽  
pp. 440-450 ◽  
Author(s):  
A. Ishibashi ◽  
T. Yokote ◽  
H. Yoshino
Keyword(s):  
Friction Coefficient ◽  
Contact Surface ◽  
Small Area ◽  
Testing Machine ◽  
Contact Forces ◽  
Appreciable Increase ◽  
Metallic Contacts ◽  
Contact Surfaces

This work was conducted to discover the highest pitting limits of the contact surfaces under combined rolling/sliding conditions. Appreciable increases in pitting limits were obtained in rollers with hardnesses in the range 190 to 335 HB using an improved testing machine made by the authors. The allowable contact forces corresponding to the new pitting limits were about four times greater than those corresponding to the earlier pitting limits. Some factors which might prevent appreciable increases in pitting limits were examined and a new experiment was conducted using rollers with a pit-producing ability limited to a small area of less than 0.1 percent of whole contact surface of the rollers. It was found that the local metallic contacts which cause only a slight increase in the friction coefficient can bring about severe pitting failure before 107 rotations.

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