scholarly journals Diagnostics of the presence of a fatigue crack in the compressor blade using the spectrum of vibration amplitudes at the superharmonic resonance

2021 ◽  
pp. 50-54
Author(s):  
Kyrylo Savchenko ◽  
Anatoliy Zinkovskiy ◽  
Eugeniia Onishchenko ◽  
Vadym Kruts ◽  
Sergii Kabannyk
Keyword(s):  
Fatigue Crack ◽  
Forced Vibration ◽  
Amplitude Ratio ◽  
Leading Edge ◽  
Compressor Blade ◽  
Sharp Change ◽  
Convex Side ◽  
Structural Element ◽  
Superharmonic Resonance ◽  
Root Edge

In this study, the solution of the forced vibration response of a structural element with a fatigue crack was carried out using the finite element method to determine the influence of its presence on the flexural forced vibration behaviour of the compressor blade airfoil at the superharmonic resonance of the order 1/2. The blade airfoil with a low twisted angle was used as an object of investigation to perform the computational analysis. Its vibrations in the plane of minimum stiffness were excited by the kinematic displacement of root edge elements. The fatigue crack was modelled as a mathematical cut. Two locations of the crack were investigated – on the leading edge and convex side of the blade airfoil. The nonlinearity due to the intermittent contact of the crack surfaces, which is caused by the opening and closing of the crack during each vibration cycle, was taken into account by solving the contact problem. To quantify this kind of nonlinear dynamic behaviour, the vibration diagnostic parameter was defined as the displacement amplitude ratio of the dominant harmonics at the superharmonic resonance of the order 1/2. Based on the results of the calculations it has been found that regardless of the crack location, the ratio nature is the same for all vibration axes. However, with vibrations in the plane of minimum stiffness, the crack on the convex side of the airfoil has an opening mode propagation, which makes it possible to fix its location due to a sharp change in the ratio of the amplitudes of the dominant harmonics along the corresponding axis.

scholarly journals Grid Dependency Study for the NASA Rotor 37 Compressor Blade

1997 ◽  
Author(s):  
Andrea Arnone ◽  
Ennio Carnevale ◽  
Michele Marconcini
Keyword(s):  
Total Pressure ◽  
Turbulence Modeling ◽  
Leading Edge ◽  
Substantial Improvement ◽  
Compressor Blade ◽  
Computational Domain ◽  
Temperature Ratio ◽  
Turbulent Transition ◽  
Total Temperature ◽  
The Impact

The NASA Rotor 37 has been computed by several authors in the last few years with relative success. The aim of this work is to present a systematic grid dependency study in order to quantify the amount of uncertainty that comes from the grid density. The computational domain is divided onto several regions (i.e. leading edge, trailing edge, shear layer …) and for each of them, the impact of the grid density is investigated. By means of this analysis, substantial improvement has been obtained in the prediction of efficiency and exit angle. On the contrary, the improvement achieved in total pressure and total temperature ratio is less remarkable. It is believed that only after a systematic grid dependency study can the contribution of turbulence modeling, laminar-turbulent transition, and boundary conditions be analyzed with success.

Study on the Stability of Non-Structural Element Using Active Tuned Mass Damper

2020 ◽  
Vol 17 (7) ◽  
pp. 3224-3230
Author(s):  
Hong-Won Kim ◽  
Dong-Gi Kwag
Keyword(s):  
High Frequency ◽  
Seismic Waves ◽  
Passive Control ◽  
Control Method ◽  
Amplitude Ratio ◽  
Vibration Reduction ◽  
Tuned Mass Damper ◽  
Structural Element ◽  
High Frequency Region ◽  
Mass Damper

Currently, the frequency of earthquakes is increasing in Korea, but due to the lack of appropriate seismic equipment, significant damage is expected. In order to solve this problem, active tuned mass damper will be developed to reduce earthquake damage in response to seismic waves, which are combined from low frequency to high frequency. In this paper, various control methods are introduced to reduce the amplitude ratio occurring at the 1st and 2nd natural frequencies for 3 DOF nonstructural elements. Through mathematical modeling, we confirm how each control method is applied and present the problems of the existing passive tuned mass damper and suggest the active tuned mass damper. To induce an active copper reducer, the response according to the control method can be predicted with a focus on the energy change rate. The active controller receives feedback from the relative displacement and relative velocity of the structure and uses it as a variable to set the control method. The passive control method and the active control method are compared through the simulation, and excellent control performance can be confirmed in the high frequency region as well as the second natural frequency. Vibration reduction performance was confirmed by each control method and the most ideal control method was selected. The optimum vibration reduction performance can be confirmed by using the signal function to always generate 180° of phase difference with respect to the speed of the structure. Not only earthquake but also mechanical vibration, wind load, etc., it can be used in all fields where damage is caused by excitation force inherent in various complex frequencies.

scholarly journals Kinematic and Moisture Characteristics of a Nonprecipitating Cold Front Observed during IHOP. Part I: Across-Front Structures

2008 ◽  
Vol 136 (1) ◽  
pp. 147-172 ◽  
Author(s):  
Katja Friedrich ◽  
David E. Kingsmill ◽  
Cyrille Flamant ◽  
Hanne V. Murphey ◽  
Roger M. Wakimoto
Keyword(s):  
Cold Front ◽  
Microwave Radiometer ◽  
Gravity Current ◽  
Leading Edge ◽  
Wide Band ◽  
Sharp Change ◽  
Air Mass ◽  
Dry Air ◽  
Early Afternoon ◽  
Variable Nature

Abstract A wide array of ground-based and airborne instrumentation is used to examine the kinematic and moisture characteristics of a nonprecipitating cold front observed in west-central Kansas on 10 June 2002 during the International H2O Project (IHOP). This study, the first of two parts, is focused on describing structures in the across-front dimension. Coarsely resolved observations from the operational network and dropsondes deployed over a 200-km distance centered on the front are combined with higher-resolution observations from in situ sensors, Doppler radars, a microwave radiometer, and a differential absorption lidar that were collected across a ∼40-km swath that straddled a ∼100-km segment of the front. The northeast–southwest-oriented cold front moved toward the southeast at ∼8–10 m s−1 during the morning hours, but its motion slowed to less than 1 m s−1 in the afternoon. In the early afternoon, the cold front separated cool air with a northerly component flow of 2–4 m s−1 from a 10-km-wide band of hot, dry air with 5 m s−1 winds out of the south-southwest. The average updraft at the frontal interface was ∼0.5 m s−1 and slightly tilted back toward the cool air. A dryline was located to the southeast of the front, separating the hot, dry air mass from a warm, moist air mass composed of 10 m s−1 southerly winds. Later in the afternoon, the warm, moister air moved farther to the northwest, approaching the cold front. The dryline was still well observed in the southwestern part of the observational domain while it vanished almost completely in the northeastern part. Low-level convergence (∼1 × 10−3 s−1), vertical vorticity (∼0.5 × 10−3 s−1), and vertical velocity (∼1 m s−1) increased. The strong stable layer located at ∼2.0–2.5 km MSL weakened in the course of the afternoon, providing a basis for the development of isolated thunderstorms. The applicability of gravity current theory to the cold front was studied. There was evidence of certain gravity current characteristics, such as Froude numbers between 0.7 and 1.4, a pronounced feeder flow toward the leading edge, and a rotor circulation. Other characteristics, such as a sharp change in pressure and lobe and cleft structures, remain uncertain due to the temporally and spatially variable nature of the phenomenon and the coarse resolution of the measurements.

Effect of Dissimilar Leading Edges on the Flow Structures Around a Square Cylinder

2015 ◽  
Vol 137 (6) ◽  
Author(s):  
R. Ajith Kumar ◽  
K. Arunkumar ◽  
C. M. Hariprasad
Keyword(s):  
Amplitude Ratio ◽  
Vortex Formation ◽  
Leading Edge ◽  
Wake Flow ◽  
Practical Significance ◽  
Flow Structures ◽  
Square Cylinder ◽  
Near Wake ◽  
Study Results ◽  
Leading Edges

In the present study, results of a flow visualization study on the flow around a square cylinder with dissimilar leading edges are presented. The radii of the leading edges of the cylinder “r1” and “r2” are such that the ratio r1/r2 is systematically varied from 0 to 1. The flow structures around the cylinder with different leading edge radii particularly the vortex shedding mode and mechanism are investigated. For studies with stationary as well as oscillated cylinder cases, the results are taken at a Reynolds number value of 2100. For the oscillated case, a special mechanism is made to oscillate the cylinders at a desired amplitude and frequency. That is, the cylinder undergoes forced oscillation in this case. Results indicate that dissimilar leading edges bring notable changes in the near-wake flow structures of a square cylinder. For the stationary cylinder cases, the vortex formation length decreases with increase in the r1/r2 ratio. Flow structures are also found to be influenced by the amplitude ratio (amplitude to body size ratio); the higher the amplitude, the larger the size of vortices shed per cycle of cylinder oscillation. In view of marine structures and building sections with similar geometries, the present results carry considerable practical significance.

The Measurement of Boundary Layers on a Compressor Blade in Cascade: Part 4 — Flow Fields for Incidence Angles of −1.5 and −8.5 Degrees

1989 ◽  
Author(s):  
W. C. Zierke ◽  
S. Deutsch
Keyword(s):  
Boundary Layers ◽  
Separation Bubble ◽  
Measurement Techniques ◽  
Leading Edge ◽  
Compressor Blade ◽  
Laser Doppler ◽  
Laser Doppler Velocimeter ◽  
Suction Surface ◽  
Laminar Separation ◽  
Pressure Surface

Measurements, made with laser Doppler velocimetry, about a double-circular-arc compressor blade in cascade are presented for −1.5 and −8.5 degree incidence angles and a chord Reynolds number near 500,000. Comparisons between the results of the current study and those of our earlier work at a 5.0 degree incidence are made. It is found that in spite of the relative sophistication of the measurement techniques, transition on the pressure surface at the −1.5 degree incidence is dominated by a separation “bubble” too small to be detected by the laser Doppler velocimeter. The development of the boundary layers at −1.5 and 5.0 degrees are found to be similar. In contrast to the flow at these two incidence angles, the leading edge separation “bubble” is on the pressure surface for the −8.5 degree incidence. Here, all of the measured boundary layers on the pressure surface are turbulent — but extremely thin — while on the suction surface, a laminar separation/turbulent reattachment “bubble” lies between roughly 35% and 60% chord. This “bubble” is quite thin, and some problems in interpreting backflow data.

A Nondestructive Strategy for the Distinction of Natural Fatigue and Stress Corrosion Cracks Based on Signals From Eddy Current Testing

2006 ◽  
Vol 129 (4) ◽  
pp. 719-728 ◽  
Author(s):  
Zhenmao Chen ◽  
Ladislav Janousek ◽  
Noritaka Yusa ◽  
Kenzo Miya
Keyword(s):  
Fatigue Crack ◽  
Stress Corrosion ◽  
Eddy Current ◽  
Amplitude Ratio ◽  
Threshold Value ◽  
Eddy Current Testing ◽  
Current Testing ◽  
Test Pieces ◽  
Induce Eddy Current ◽  
Good Possibility

In this paper, a novel nondestructive strategy is proposed for distinguishing differences between a stress corrosion crack (SCC) and a fatigue crack (FC) based on signals from eddy current testing (ECT). The strategy consists of measurement procedures with a special ECT probe and crack type judgment scheme based on an index parameter that is defined as the amplitude ratio of the measured signals. An ECT probe, which can induce eddy current flowing mainly in a selected direction, is proposed and applied to detect crack signals by scanning along the crack with different probe orientations. It is clear that the ratio of the amplitudes of signals detected for parallel and perpendicular probe orientations is sensitive to the microstructure of the crack, i.e., the parameter is much bigger for a fatigue crack than that of a SCC. Therefore, whether a crack is a SCC or a FC can be recognized nondestructively by comparing the index parameter with a threshold value that can be previously determined. In order to verify the validity of the proposed strategy, many artificial SCC and FC test pieces were fabricated and ECT inspections were performed to measure the corresponding crack signals. Numerical simulations were also conducted to investigate the physical principles of the new methodology. From both the numerical and experimental results, it is demonstrated that the strategy is very promising for the distinction of artificial SCC and FC; there is also good possibility that this method can be applied to natural cracks if the threshold value can be properly determined.

Simulation and Experimental Analysis of Fatigue Crack Growth under Cyclic Loading

2011 ◽  
Vol 462-463 ◽  
pp. 501-505
Author(s):  
S.M. Beden ◽  
Shahrum Abdullah ◽  
Ahmad Kamal Ariffin ◽  
N.A. Al-Asady
Keyword(s):  
Growth Rate ◽  
Fatigue Crack ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Fatigue Crack Growth Rate ◽  
Growth Models ◽  
Rate Data ◽  
Structural Elements ◽  
Structural Element

The problem of crack growth is a major issue in the prediction and maintenance of engineering structural elements. Prediction of expected life of a structural element due to constant (static) and alternating loading (fatigue) is of major concern to the designers. Prediction of remaining life of the structural elements influences the decisions of maintenance engineers (checking intervals, corrections, and replacements).The fatigue crack growth rate, which determine the fatigue life of the components after crack initiation need to be experimentally and theoretically investigated. In this study, fatigue crack growth tests were conducted under constant amplitude loading at a stress ratio of 0.1, using three-point bend (TPB) specimens of ASTM A533 steel material. For the simulation part of this study, three fatigue crack growth models, i.e. the Paris, modified Forman and Austen were examined. None of the models has a fit for the fatigue crack growth rate data in a similar behaviour compared to others. The modified Forman model provided a closer fit than the Paris model with respect to the experimental results. However, the Austen model provided the best fit to the fatigue crack growth rate data as compared with the other two models. Therefore, this model is suggested for use in critical applications.

scholarly journals Influence of the Cyclic Hardening Model on the Results of the Numerical Analysis of Fatigue Life on Example of the Compressor Blade

2019 ◽  
Vol 26 (2) ◽  
pp. 7-14
Author(s):  
Arkadiusz Bednarz
Keyword(s):  
Numerical Analysis ◽  
Leading Edge ◽  
Experimental Tests ◽  
Cyclic Hardening ◽  
Load Cycle ◽  
Geometrical Model ◽  
Fatigue Tests ◽  
Compressor Blade ◽  
Hardening Model ◽  
The Impact

Abstract The main goal of the presented work is to determine the impact of the cyclic hardening model on the numerical results of the ε-N fatigue test. As an object of study, compressor blade (from PZL-10W helicopter engine) was used. The examined blade was made of EI-961 alloy. In numerical analysis, a geometrical model of the blade with a preliminary defect was created. Geometrical defect – V-notch was created on the leading edge. This defect was introduced in order to weaken the structure of the element and the possibility of observing the crack initiation process (in experimental tests). Material data to ε-N analysis, based on Manson-Coffin-Basquin equation, were estimated for Mitchell’s model. This model was built based on strength data provided by the steel producer. Based on three different models of cyclic hardening (Manson, Fatemi, and Xianxin), a number of load cycles were calculated. Load cycle during numerical analysis was represented as resonance bending with an amplitude of displacement equal to A = 1.8 mm. Obtained results were compared with experimental data. Additionally, the analytical model of ε-N fatigue (depending on the cyclic hardening) was prepared. All the work carried out has been summarized by a comprehensive comparative analysis of the results. Obtained results and dependencies can be used in the selection of an appropriate model of cyclic hardening in further fatigue tests of many aerospace elements.

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