scholarly journals The Effect of Non-Conservative Compressive Force on the Vibration of Rotating Composite Blades

Vibration ◽  
2020 ◽  
Vol 3 (4) ◽  
pp. 478-490
Author(s):  
Mohammadreza Amoozgar ◽  
Mahdi Bodaghi ◽  
Rafic M. Ajaj
Keyword(s):  
Dynamic Behavior ◽  
Nonlinear Differential Equations ◽  
Compressive Force ◽  
Rotor Blades ◽  
Axial Compressive Force ◽  
Composite Blade ◽  
Vibration Behavior ◽  
Time Space ◽  
Blade Tip ◽  
Composite Blades

This paper investigates the effectiveness of a resonance avoidance concept for composite rotor blades featuring extension–twist elastic coupling. The concept uses a tendon, attached to the tip of the blade, to apply a proper amount of compressive force to tune the vibration behavior of the blade actively. The tendon is simulated by applying a non-conservative axial compressive force applied to the blade tip. The main load carrying part of the structure is the composite spar box, which has an antisymmetric layup configuration. The nonlinear dynamic behavior of the composite blade is modelled by using the geometrically exact fully intrinsic beam equations. The resulting nonlinear differential equations are discretized using a time–space scheme, and the stationary and rotating frequencies of the blade are obtained. It is observed that the proposed resonance avoidance mechanism is effective for tuning the vibration behavior of composite blades. The applied compressive force can shift the frequencies and the location at which the frequency veering take place. Furthermore, the compressive force can also cause the composite blade to get unstable depending on the layup ply angle. Finally, the results, highlighting the importance of compressive force and ply angle on the dynamic behavior of composite blades, are presented and discussed.

Study of Rotor Blades Vibration Behavior of Counter Rotating Fan Models

2014 ◽  
Author(s):  
A. Stepanov ◽  
V. Fateev ◽  
V. Mileshin
Keyword(s):  
Rotor Blade ◽  
Rotor Blades ◽  
Test Facility ◽  
Strain Gauges ◽  
Contactless Method ◽  
Blade Vibration ◽  
Vibration Behavior ◽  
Vibration Parameters ◽  
The Impact ◽  
Composite Blades

Three test campaigns were carried out at CIAM C-3A test facility (Turaevo, Russia) with the aim of investigating aerodynamic and acoustic performances of three counter rotating fan models under the European VITAL project [1–3]. The second fan configuration CRTF2a [2] differs from the reference fan configuration CRTF1 by thickened blades profiling designed for simulation the composite blades. The third version of counter rotating fan model CRTF2b [4] was manufactured according to “blisk” technology to simulate composite blades. Along with studies of aerodynamic and acoustic performances of fan models, the C-3A test facility provides an opportunity to investigate and estimate the rotor blades vibration behavior. The rotor blade as the most loaded fan component, experiences the impact of various types of flow disturbances leading to its resonance vibrations and sometimes creating conditions for initiation of flutter at rotor blade natural frequencies. This is the reason for extending the information content of the measurements, improvement the measurement tools and methodology. The contactless method of blade vibration measurements (tip-timing) was used on the basis of MIC-DPM equipment («Mera» Research and Production Enterprise, Russia) [5,6] in combination with a traditional technique of strain gauges installation for determination of counter rotating fan rotor blades vibration behavior. This work presents the description of applied methodologies for measurements of rotor blades vibration parameters. Additionally, the paper presents the measurement results of rotor blades vibration behavior for three counter rotating fan models studied by means of a strain gauges technique and a contactless blade tip-timing method as well as the comparison analysis of numerical and experimental results in relation to vibration behavior of tested fan models.

Influence of a Cylindrical Exhaust Hood Installation on the Last Stage Rotor Blades of a Low Pressure Model Steam Turbine

2017 ◽  
Author(s):  
Fabian F. Müller ◽  
Markus Schatz ◽  
Damian M. Vogt ◽  
Jens Aschenbruck
Keyword(s):  
Flow Field ◽  
Steam Turbine ◽  
Operating Conditions ◽  
Rotor Blades ◽  
Pressure Measurements ◽  
Exhaust Hood ◽  
Blade Vibration ◽  
Time Resolved ◽  
Vibration Behavior ◽  
Last Stage

The influence of a cylindrical strut shortly downstream of the bladerow on the vibration behavior of the last stage rotor blades of a single stage LP model steam turbine was investigated in the present study. Steam turbine retrofits often result in an increase of turbine size, aiming for more power and higher efficiency. As the existing LP steam turbine exhaust hoods are generally not modified, the last stage rotor blades frequently move closer to installations within the exhaust hood. To capture the influence of such an installation on the flow field characteristics, extensive flow field measurements using pneumatic probes were conducted at the turbine outlet plane. In addition, time-resolved pressure measurements along the casing contour of the diffuser and on the surface of the cylinder were made, aiming for the identification of pressure fluctuations induced by the flow around the installation. Blade vibration behavior was measured at three different operating conditions by means of a tip timing system. Despite the considerable changes in the flow field and its frequency content, no significant impact on blade vibration amplitudes were observed for the investigated case and considered operating conditions. Nevertheless, time-resolved pressure measurements suggest that notable pressure oscillations induced by the vortex shedding can reach the upstream bladerow.

Effect of Coulomb Damping on Buckling of a Simply Supported Beam

1999 ◽  
Author(s):  
H. Yabuno ◽  
R. Oowada ◽  
N. Aoshima
Keyword(s):  
Compressive Force ◽  
Pitchfork Bifurcation ◽  
Steady States ◽  
Initial Condition ◽  
Axial Compressive Force ◽  
Simply Supported Beam ◽  
Simply Supported ◽  
Coulomb Damping ◽  
Buckling Behavior ◽  
Equilibrium Region

Abstract The present work describes a significant influence of a slight Coulomb damping on buckling of the simply supported beam subjected to an axial compressive force. Coulomb damping in the supporting points produces equilibrium regions around the well-known stable and unstable steady states under the pitchfork bifurcation which are analytically obtained in no consideration of the effect of Coulomb damping. After the transient response, the beam can stop any states in the equilibrium region, which becomes wider in the vicinity of the bifurcation point, depending on the initial condition. Also, the imperfection due to gravity is considered and it is theoretically shown that the equilibrium region is connected in the case when the imperfection due to gravity is relatively small comparing with the effect of the Coulomb damping, while the steady states under the pitchfork bifurcation in no consideration of the effect of Coulomb damping are necessarily disconnected by imperfection. Experimental results confirm the theoretically predicted effect of Coulomb damping in the supporting point on the buckling behavior of the beam.

Biomechanical Study of Lumbar Spine (L2-L4) Using Hybrid Stabilization Device - A Finite Element Analysis

2020 ◽  
Vol 10 (1) ◽  
pp. 20-32 ◽  
Author(s):  
Pushpdant Jain ◽  
Mohammed Rajik Khan
Keyword(s):  
Finite Element ◽  
Compressive Force ◽  
Element Model ◽  
Biomechanical Study ◽  
Bottom Surface ◽  
Element Analysis ◽  
Axial Compressive Force ◽  
Hybrid Stabilization ◽  
Flexion Extension ◽  
Lumbar Segment

Spinal instrumentations have been designed to alleviate lower back pain and stabilize the spinal segments. The present work aims to evaluate the biomechanical effect of the proposed Hybrid Stabilization Device (HSD). Non-linear finite element model of lumbar segment L2-L4 were developed to compare the intact spine (IS) with rigid implant (RI) and hybrid stabilization device. To restrict all directional motion vertebra L4 bottom surface were kept fixed and axial compressive force of 500N with a moment of 10Nm were applied to the top surface of L2 vertebrae. The results of range of motion (ROM), intervertebral disc (IVD) pressure and strains for IVD-23 and IVD-34 were determined for flexion, extension, lateral bending and axial twist. Results demonstrated that ROM of HSD model is higher than RI and lower as compared to IS model. The predicted biomechanical parameters of the present work may be considered before clinical implementations of any implants.

scholarly journals Biomechanical Evaluation of Suture Button Spread with and without Deltoid Repair in Combined Syndesmosis and Deltoid Injury

2020 ◽  
Vol 5 (4) ◽  
pp. 2473011420S0031
Author(s):  
Brian Lau ◽  
Hunter Storaci ◽  
Kaysie Tam ◽  
Cara Lai ◽  
Brett P. Salazar ◽  
...  
Keyword(s):  
Compressive Force ◽  
Joint Line ◽  
Joint Surface ◽  
Axial Compressive Force ◽  
Ankle Motion ◽  
Posterior Displacement ◽  
Intact State ◽  
Suture Button ◽  
Syndesmosis Injury ◽  
Injury And Repair

Category: Sports; Basic Sciences/Biologics Introduction/Purpose: Syndesmosis injuries are common and frequently occur with deltoid injuries but optimal repair remains controversial. Prior biomechanical studies have demonstrated that 1 and 2 suture buttons are equivalent to screw fixation and that parallel or divergent suture buttons are equivalent to single suture button. Prior studies, however, created constructs with suture buttons within 1cm from each other (2-3cm from joint surface). Additionally, the role of deltoid injury and repair have not been evaluated in conjunction with syndesmosis injury and repair. The purpose of this study was to biomechanically compare a narrow vs spread 2-suture button construct with and without a deltoid repair. Methods: Four matched lower leg specimens (8 total specimens) aged mean 60.2 years (range 57-66 years; 6 females and 2 males; mean BMI 21.1) were tested. Ankle motion under cyclic loading was measured in multiple planes: first in the intact state, following simulated syndesmosis and deltoid injury, then following fixation with 1 of 2 randomly assigned constructs: 2 parallel suture buttons at 2 and 3cm from joint line (narrow); and 2 parallel suture buttons at 1 and 4cm from joint line (spread), and then finally following a deltoid repair with each construct. Each state was tested at a constant 750 N axial compressive force and 5N internal/external torque. Rotation position (degrees) and anterior-posterior displacement (mm) were collected throughout the testing to characterize relative spatial relationships of the tibiofibular articulation using 3D video capture technology. Results: Narrow and spread 2-suture button constructs improved rotation and translation compared to cut state (p<0.05) but not to intact state (p>0.05). There were no significant differences in rotation or translation between Narrow and Spread constructs (p>0.05). The addition of a deltoid repair did not improve rotation or translation compared to syndesmosis repair with either construct alone (p>0.05). Conclusion: The preliminary results of this study suggest that constructs with suture button placed close together or spread apart during fixation of combined syndesmosis and deltoid injury could improve rotation and translation equally. Additionally, in a combined syndesmosis and deltoid injury, the addition of a deltoid repair to a syndesmosis repair did not strengthen the construct. These findings suggest that repair of syndesmosis alone may be sufficient in combined syndesmosis and deltoid injuries. Additional matched samples will be tested to validate preliminary findings.

Numerical Investigation of Tip Clearance Flow Induced Flutter in an Axial Research Compressor

2016 ◽  
Author(s):  
Daniel Möller ◽  
Maximilian Jüngst ◽  
Felix Holzinger ◽  
Christoph Brandstetter ◽  
Heinz-Peter Schiffer ◽  
...  
Keyword(s):  
Early Stage ◽  
Rotor Blades ◽  
Tip Clearance ◽  
Blade Vibration ◽  
Tip Clearance Flow ◽  
Transonic Compressor ◽  
Clearance Flow ◽  
Fluctuation Pattern ◽  
Blade Tip ◽  
Pass Through

A flutter phenomenon was observed in a 1.5-stage configuration at the Darmstadt transonic compressor. This phenomenon is investigated numerically for different compressor speeds. The flutter occurs for the second eigenmode of the rotor blades and is caused by tip clearance flow which is able to pass through multiple rotor gaps at highly throttled operating points. The vibration pattern during flutter is accompanied by a pressure fluctuation pattern of the tip clearance flow which is interacting with the blade motion causing the aeroelastic instability. The velocity of the tip clearance flow fluctuation is about 50% of the blade tip speed for simulation and experiment and also matches the mean convective velocity inside the rotor gap. This is consistent for all compressor speeds. From this investigations, general guidelines are drawn which can be applied at an early stage during compressor design to evaluate the susceptibility to this kind of blade vibration.

Analysis of Free Nonlinear Vibration Behavior for Curved Embedded Carbon Nanotubes on Elastic Foundation

2010 ◽  
Author(s):  
M. Rezaee ◽  
H. Fekrmandi
Keyword(s):  
Carbon Nanotubes ◽  
Dynamic Behavior ◽  
Continuum Mechanics ◽  
Nonlinear Term ◽  
Nonlinear Oscillations ◽  
Equation Of Motion ◽  
System Response ◽  
Response Curves ◽  
Vibration Behavior ◽  
The Continuum

Carbon nanotubes (CNTs) are expected to have significant impact on several emerging nanoelectromechanical (NEMS) applications. Vigorous understanding of the dynamic behavior of CNTs is essential for designing novel nanodevices. Recent literature show an increased utilization of models based on elastic continuum mechanics theories for studying the vibration behavior of CNTs. The importance of the continuum models stems from two points; (i) continuum simulations consume much less computational effort than the molecular dynamics simulations, and (ii) predicting nanostructures behavior through continuum simulation is much cheaper than studying their behavior through experimental verification. In numerous recent papers, CNTs were assumed to behave as perfectly straight beams or straight cylindrical shells. However, images taken by transmission electron microscopes for CNTs show that these tiny structures are not usually straight, but rather have certain degree of curvature or waviness along the nanotubes length. The curved morphology is due to process-induced waviness during manufacturing processes, in addition to mechanical properties such as low bending stiffness and large aspect ratio. In this study the free nonlinear oscillations of wavy embedded multi-wall carbon nanotubes (MWCNTs) are investigated. The problem is formulated on the basis of the continuum mechanics theory and the waviness of the MWCNTs is modeled as a sinusoidal curve. The governing equation of motion is derived by using the Hamilton’s principle. The Galerkin approach was utilized to reduce the equation of motion to a second order nonlinear differential equation which involves a quadratic nonlinear term due to the curved geometry of the beam, and a cubic nonlinear term due to the stretching effect. The system response has been obtained using the incremental harmonic balanced method (IHBM). Using this method, the iterative relations describing the interaction between the amplitude and the frequency for the single-wall nanotube and double-wall nanotube are obtained. Also, the influence of the waviness, elastic medium and van der Waals forces on frequency-response curves is researched. Results present some useful information to analyze CNT’s nonlinear dynamic behavior.

Experimental Investigations Into Pressure Field in Tip Clearance of Shrouded Rotor Blades

2002 ◽  
Author(s):  
Krzysztof Kosowski ◽  
Marian Piwowarski
Keyword(s):  
Pressure Distribution ◽  
Pressure Pulsation ◽  
Pressure Field ◽  
Rotor Blades ◽  
Tip Clearance ◽  
Experimental Investigations ◽  
Pressure Pulsations ◽  
Blade Tip ◽  
Shrouded Rotor ◽  
Blade Tip Clearance

The experimental investigations into the pressure field in the shroud clearance were performed on a one-stage air model turbine of impulse type. Measurements of pressure distribution were carried out for different rotor eccentricities, different values of axial gap and of rotor-stator misalignment, different rotor speeds and different turbine load. The experimental investigations proved that: a) the pressure in the blade tip clearance is not stationary but it pulsates, b) the effect of nozzle trailing edge can be observed in the blade shroud clearance, c) for a given turbine output, the rotor-stator eccentricity and rotor-stator misalignment appear the most important parameters influencing the pressure distribution in the shroud clearance. Aiming to investigate the pressure pulsation transmission through the leakage flow in the blade shroud clearances, pulsations of different amplitudes and frequencies were excited in the turbine inlet duct and corresponding changes of pressure were measured along the shroud width, followed by appropriate harmonic analysis. The investigations were performed for forced pulsations with frequencies ranging from 1Hz to 8 Hz. In all the examined cases, the frequency of pressure pulsations remained unchanged, while the amplitude of the pulsation decreased gradually along the tip clearance. The frequency of these pressure pulsations in the tip clearance was equal to the frequency of the pressure pulsation at the turbine stage inlet and to the frequency of pressure pulsation at the turbine flow passage’s exit.

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