Double Nodal Diameter Spectrum Method and its Application in Quantification of Vibration Localization of Impellers With Splitter Blades

2017 ◽  
Author(s):  
Kaicheng Liu ◽  
Jianjun Wang
Keyword(s):  
Travelling Wave ◽  
Mode Shapes ◽  
Response Analysis ◽  
Nodal Diameter ◽  
Mode Localization ◽  
Vibration Localization ◽  
Engine Order ◽  
Vibration Pattern ◽  
Harmonic Response Analysis ◽  
Definition Of

Double nodal diameter spectrum (DNDS) method which is used to analyze nodal diameter (ND) components of the vibration modes of impellers with splitters is proposed and its application in quantification of mode localization has been studied. Firstly, ND characteristics of the typical impeller with splitter blades are analyzed by mode shapes and representative subeigenvectors. Secondly, DNDS method is proposed and DNDSs of the representative modes indicate that the tuned modes of impellers with splitter blades contain two ND components. By applying the simplified engine order (EO) excitation in the form of a travelling wave, harmonic response analysis has been carried out by which double nodal diameter vibration characteristics of the structure and the effectiveness of the DNDS method are both validated. Lastly, in terms of quantifying mode localization, the definition of mode localization factor (MLF) is improved based on DNDS. The numerical example proves that the pairing process of choosing the tuned mode corresponding to the mistuned one by utilizing both DNDS and the vibration pattern of blades when calculating the improved MLF could pick out the closest tuned mode to the mistuned one, which has a more explicit physical meaning.

The Harmonic Response Analysis of Engine Block Based on Modal Analysis

2011 ◽  
Vol 138-139 ◽  
pp. 246-251 ◽  
Author(s):  
Zhong Cai Zheng ◽  
Yan Gao ◽  
Na Liu ◽  
Kun Jin Zhang ◽  
Hai Ou Chen ◽  
...  
Keyword(s):  
Finite Element Method ◽  
Modal Analysis ◽  
Engine Block ◽  
Mode Shapes ◽  
Response Analysis ◽  
Frequency Curve ◽  
Harmonic Response ◽  
Harmonic Response Analysis ◽  
Block Based ◽  
Typical Mode

The modal analysis of the engine block is carried out using finite element method. Through the analysis, the inherent frequencies and mode shapes of the first 6 order modes are obtained respectively. Then the harmonic response analysis of the engine block is carried out based on the modal analysis, and the corresponding inherent frequencies of the weak positions of block under the action of external cycle force are obtained. Finally, the consistency of the typical mode shape and amplitude-frequency curve is compared.

scholarly journals An Experimental Investigation of Vibration Localization in Bladed Disks: Part II — Forced Response

1997 ◽  
Author(s):  
Marlin J. Kruse ◽  
Christophe Pierre
Keyword(s):  
Experimental Investigation ◽  
Forced Response ◽  
Mode Shapes ◽  
Bladed Disks ◽  
Structural Coupling ◽  
Vibration Localization ◽  
Bladed Disk ◽  
Engine Order ◽  
Localized Mode ◽  
The Impact

The results of an experimental investigation on the effects of random blade mistuning on the forced dynamic response of bladed disks are reported. Two experimental specimens are considered: a nominally periodic twelve-bladed disk with equal blade lengths, and the corresponding mistuned bladed disk, which features slightly different blades of random lengths. Both specimens are subject to traveling-wave excitations delivered by piezo-electric actuators. The primary aim of the experiment is to demonstrate the occurrence of an increase in forced response blade amplitudes due to mistuning, and to verify analytical predictions about the magnitude of these increases. In particular, the impact of localized mode shapes, engine order excitation, and disk structural coupling on the sensitivity of forced response amplitudes to blade mistuning is reported. This work reports one of the first systematic experiments carried out to demonstrate and quantify the effect of mistuning on the forced response of bladed disks.

Investigation of Alternate Mistuned Turbine Blades Non-Linear Coupled by Underplatform Dampers

2013 ◽  
Author(s):  
S. Tatzko ◽  
L. Panning-von Scheidt ◽  
J. Wallaschek ◽  
A. Kayser ◽  
G. Walz
Keyword(s):  
Turbine Blades ◽  
Forced Response ◽  
Mode Shapes ◽  
Nodal Diameter ◽  
Frictional Contacts ◽  
Bladed Disk ◽  
Engine Order ◽  
Bladed Disk Assembly ◽  
Last Stage ◽  
Software Code

Freestanding turbine blades have typically low structural damping and thus require additional friction damping devices, such as underplatform dampers. The friction coupling between neighboring blades reduces response amplitude and increases resonance frequency. Along with forced response excitation large blades, especially of last stage, could be excited by fluid structural interaction (flutter). To prevent such excitation alternate mistuned blade patterns are beneficial disturbing traveling waves in the stage. In this paper the influence of alternate mistuning is investigated with a simplified oscillator chain as well as a bladed disk assembly coupled by frictional contacts. It is pointed out that the performance of friction coupling can be improved by alternate mistuning as long as the engine order of the excitation is below quarter of the number of blades. Alternate mistuning causes a mode coupling between two nodal diameter vibration mode shapes allowing for energy transfer. The in-house developed software code DATAR is enhanced and alternate mistuning can be applied to the blades as well as to the damping elements. For validation the DATAR code was applied to an alternate mistuned last stage blade of a Siemens gas turbine and compared with available field engine measurement.

The Finite Element Analysis of Vibrating Screen

2011 ◽  
Vol 141 ◽  
pp. 134-138
Author(s):  
Chuan Guang Ding ◽  
Fang Zhen Song ◽  
Bo Song ◽  
Xiu Hua Men
Keyword(s):  
Large Scale ◽  
Natural Frequencies ◽  
Modular Design ◽  
Mode Shapes ◽  
Response Analysis ◽  
Element Analysis ◽  
Harmonic Response ◽  
Vibrating Screen ◽  
The Finite Element Analysis ◽  
Harmonic Response Analysis

The large-scale and modular design of vibrating screen brings about the trend that the screen separate from screen frame. The separation of the screen frame and the screen changes their dynamic characteristics. By making modal analysis and harmonic response analysis in ANSYS, the dynamic data of the screen and the screen frame was obtained, such as the natural frequencies, mode shapes, stress distribution and strain distribution. The results show that the stiffness of screen frame is higher than stiffness of the screen and the side plats and beams of screen are the weak parts.

scholarly journals A Transfer Matrix Approach to Vibration Localization in Mistuned Blade Assemblies

1993 ◽  
Author(s):  
Gísli Óttarsson ◽  
Christophe Pierre
Keyword(s):  
Transfer Matrix ◽  
Design Tool ◽  
Matrix Approach ◽  
Transfer Matrices ◽  
Free Response ◽  
Mode Localization ◽  
Vibration Localization ◽  
Transfer Matrix Approach ◽  
Definition Of ◽  
Low Sensitivity

A study of mode localization in mistuned bladed disks is performed using transfer matrices. The transfer matrix approach yields the free response of a general, mono-coupled, perfectly cyclic assembly in closed form. A mistuned structure is represented by random transfer matrices, and the expansion of these matrices in terms of the small mistuning parameter leads to the definition of a measure of sensitivity to mistuning. An approximation of the localization factor, the spatially averaged rate of exponential attenuation per blade-disk sector, is obtained through perturbation techniques in the limits of high and low sensitivity. The methodology is applied to a common model of a bladed disk and the results verified by Monte Carlo simulations. The easily calculated sensitivity measure may prove to be a valuable design tool due to its system-independent quantification of mistuning effects such as mode localization.

One Exciter per Sector Test Bench for Bladed Wheels Harmonic Response Analysis

2017 ◽  
Author(s):  
Leonardo Bertini ◽  
Paolo Neri ◽  
Ciro Santus ◽  
Alberto Guglielmo
Keyword(s):  
Test Bench ◽  
Wide Frequency Range ◽  
Mode Shapes ◽  
Response Analysis ◽  
Global Mode ◽  
Loop Control ◽  
Harmonic Response ◽  
Electromagnetic Devices ◽  
Modal Damping ◽  
Harmonic Response Analysis

Bladed wheel dynamic characterization is a crucial issue to avoid resonance excitations. The test bench presented in this paper was designed to independently excite the wheel sectors with one electromagnetic shaker each blade. Since a wide frequency range (1–10 kHz) is usually considered for bladed wheels, custom electromagnetic devices were designed, and then a closed-loop control software was also implemented. The global mode shapes of the wheel were then reconstructed through subsequent accelerometer measurements on all sectors to evaluate the harmonic response. The main target of the test rig is the reproduction of any operational condition by experimentally simulating an arbitrary number of stator vanes. In this way the response levels of the differently excited modes are measured and the modal damping is optimally quantified by providing a selective excitation of any number of nodal diameters. Preliminary results showed how the test setup actually allows to excite those modes with a specific number of nodal diameters, however, also exposed some difficulties to avoid small load components with different numbers of nodal diameters.

scholarly journals FEM Based Modal and Harmonic Response Study of Stepped Shaft Having Cracks and Optimize Using ANN Method

2020 ◽  
pp. 1-12
Author(s):  
Asha Kumawat ◽  
K. B. Waghulde ◽  
Sanjay Kumawat
Keyword(s):  
Research Study ◽  
Fem Simulation ◽  
Mode Shapes ◽  
Response Analysis ◽  
Harmonic Response ◽  
Stepped Shaft ◽  
Harmonic Response Analysis ◽  
The Stability ◽  
Ss 304

In the present research study, modal and harmonic response analysis is performed for a stepped shaft made of SS-304 material using the FEM simulation technique. In the present study crack effect is also considered to find the role of cracks during modal analysis. Total six mode shapes are considered in this study and 500 N force is considered for harmonic response analysis. The simulation is performed using Ansys WB based APDL solver. The main outcome for this study is the critical speed of shaft for rotation from 10 RPM to 80K RPM, stress, deformation of the shaft without crack, and with crack. The selected shaft is stepped in nature, total length of shaft is 300 mm having three diameters of 20 mm, 40 mm, and 60 mm. The natural frequency for all six node shapes is from 1000 Hz to 4000 Hz having deformation from 15 mm to 30 mm approx for all combinations of crack in the shaft. After all simulation it is found that for all mode shapes, the stability and strength of the shaft are good during vibration conditions.

The Influence of Mistuning and Coriolis Effects on the Modal Parameters of Bladed Discs: An Experimental Study

2017 ◽  
Author(s):  
Valentina Ruffini ◽  
Jeffrey S. Green ◽  
Christoph W. Schwingshackl
Keyword(s):  
Measurement Data ◽  
Travelling Wave ◽  
Mode Shapes ◽  
Gradual Transition ◽  
Nodal Diameter ◽  
New Approach ◽  
Coriolis Effects ◽  
Accurate Comparison ◽  
High Level ◽  
Different Levels

A very detailed experimental analysis at several different rotational speeds was conducted on a simplified blisk to gain in-depth understanding of how the Coriolis effects and their interaction with mistuning evolve with speed to provide a better understanding for future designs. Two different nodal diameter families, characterised by different levels of mistuning, were investigated in greater detail. The blisk dynamics were found to depend both on mistuning levels and speed. Split Campbell diagrams were observed, together with the appearance of Coriolis-induced forward and backward travelling wave modes in the blisk. Three speed ranges characterised by different behaviours were identified at a high level of detail, with a gradual transition from mistuning-dominated behaviour at low speed to Coriolis-dominated features at higher speeds. The evolution of the mode shapes with speed, and the differences between low- and high-mistuning modes were particularly examined. The evolution of the mode shapes with speed, and the differences between low- and high-mistuning modes were particularly examined. An accurate comparison was conducted between the measurement data and finite element results, and confirmed the reliability of the new approach.

scholarly journals Tip-Timing Measurements and Numerical Analysis of Last-Stage Steam Turbine Mistuned Bladed Disc During Run-Down

2019 ◽  
Vol 8 (3) ◽  
pp. 409-415 ◽  
Author(s):  
Romuald Rzadkowski ◽  
Leszek Kubitz ◽  
Michał Maziarz ◽  
Pawel Troka ◽  
Krzysztof Dominiczak ◽  
...  
Keyword(s):  
Steam Turbine ◽  
Natural Frequencies ◽  
Timing Analysis ◽  
Mode Shapes ◽  
Fe Model ◽  
Blade Vibration ◽  
Nodal Diameter ◽  
Mode Localization ◽  
Numerical Studies ◽  
Last Stage

Abstract Background This paper presents the experimental and numerical studies of last-stage low-pressure (LP) mistuned steam turbine bladed discs during run-down. Methods The natural frequencies and mode shapes of the turbine bladed disc were calculated using an FE model. The influence of the shaft on the modal properties, such as natural frequencies and mode shapes, was considered. The tip-timing method was used to find the mistuned bladed disc modes and frequencies. Conclusions The experimental results from the tip-timing analysis show that the mistuning in combination with shaft coupling suppresses pure nodal diameter type blade vibrations associated with the fundamental mode shape of a cantilevered blade. Vibration modes emerge when even a single blade is vibrating due to the well-known mode localization caused by mistuning. The numerical results confirm this.

scholarly journals Numerical Model on the Dynamic Behavior of a Prototype Kaplan Turbine Runner

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Ming Zhang ◽  
Qing-Guang Chen
Keyword(s):  
Experimental Results ◽  
Whole Body ◽  
Mode Shapes ◽  
Response Analysis ◽  
Kaplan Turbine ◽  
Turbine Runner ◽  
Narrow Frequency Band ◽  
Response Peak ◽  
Modal Behavior ◽  
Harmonic Response Analysis

Experimental and numerical investigations of the modal behavior of a prototype Kaplan turbine runner in air have been conducted in this paper. The widely used roving accelerometer method was used in the experimental modal analysis. A systematic approach from a single blade model to the whole runner has been used in the simulation to get a thorough understanding. The experimental results show that all the detected modes concentrate their displacements on the impacted blade. The numerical results show that the modes of the single blade form different mode families of the runner, and each mode family corresponds to a narrow frequency band. Harmonic response analysis shows that, at the response peak point, the single blade excitation can only get mode shapes with concentrations on the exciting blade due to the superposition of the close modes in each mode family, which explains the experimental results well, while the mode superposition can be avoided by the order excitation method. With the reduction of the connection stiffness between the blades and hub/control system, the frequencies of most modes change from insensitive to more and more sensitive to the connection stiffness change, which results in a sensitive area and an insensitive area. Through comparison with the experimental results, it is indicated that the natural frequencies of the runner can probably be predicted by merging the runner into a whole body.

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