The Determination of Fan Blade Aerodynamic Loading From a Measured Response

2015 ◽  
Author(s):  
Jacques Muiyser ◽  
Daniel N. J. Els ◽  
Sybrand J. van der Spuy ◽  
Albert Zapke
Keyword(s):  
Fourier Series ◽  
Strain Gauge ◽  
Full Scale ◽  
Aerodynamic Forces ◽  
Single Degree Of Freedom ◽  
Single Degree ◽  
Aerodynamic Loading ◽  
Fan Blade ◽  
Strain Gauge Measurements ◽  
Measured Response

Large-scale cooling system fans often operate under distorted inlet air flow conditions due to the presence of other fans and the prevalent wind conditions. Strain gauge measurements have been used to determine the blade loading as a result of the unsteady aerodynamic forces. However, these measurements are of the blade’s response to the aerodynamic forces and include the deformation as a result of the first natural frequency being excited. When considering the dominant first natural frequency and bending mode of the fan blade, one can approximate the fan blade as a cantilever beam that acts as a single degree-of-freedom system. The response of a single degree-of-freedom system can be calculated analytically for any excitation if the system’s properties are known. The current investigation focuses on using these equations to create an algorithm that can be applied to the measured response of a fan blade to then extract the aerodynamic forces exciting it. This is performed by using a simple non-linear, least-squares optimization algorithm to fit a complex Fourier series to the response and using the coefficients of each harmonic term to determine the Fourier series representing the excitation function. The algorithm was first tested by applying it to the response of a finite element cantilever beam representing a simplified model of the fan blade. Good results were obtained for a variety of excitation forces and as such the algorithm was then applied to the measured response of a full-scale fan blade. The full-scale blade was excited with a shaker where the forcing function could be accurately controlled. Once validated, the algorithm was applied to a set of strain gauge measurements that were recorded at a full-scale fan while in operation. The reconstructed aerodynamic loading showed increased forces when the blade passed beneath the fan bridge as well as when it approached the windward side of the casing.

Predicting the Impact Response of a Nonlinear Single-Degree-of-Freedom Shock-Absorbing System From the Measured Step Response

1997 ◽  
Vol 119 (3) ◽  
pp. 221-227 ◽  
Author(s):  
S. N. Robinovitch ◽  
W. C. Hayes ◽  
T. A. McMahon
Keyword(s):  
High Energy ◽  
Degree Of Freedom ◽  
Step Response ◽  
Single Degree Of Freedom ◽  
Single Degree ◽  
Impact Forces ◽  
Standard Linear Solid ◽  
Standard Linear ◽  
The Impact ◽  
Measured Response

We measured the step response of a surrogate human pelvis/impact pendulum system at force levels between 50 and 350 N. We then fit measured response curves with four different single-degree-of-freedom models, each possessing a single mass, and supports of the following types: standard linear solid, Voigt, Maxwell, and spring. We then compared model predictions of impact force during high-energy collisions (pendulum impact velocity ranging from 1.16 to 2.58 m/s) to force traces from actual impacts to the surrogate pelvis. We found that measured peak impact forces, which ranged from 1700 to 5600 N, were best predicted by the mass-spring, Maxwell, and standard linear solid models, each of which had average errors less than 3 percent. Reduced accuracy was observed for the commonly used Voigt model, which exhibited an average error of 10 percent. Considering that the surrogate pelvis system used in this study exhibited nonlinear stiffness and damping similar to that observed in simulated fall impact experiments with human volunteers, our results suggest that these simple models allow impact forces in potentially traumatic falls to be predicted to within reasonable accuracy from the measured response of the body in safe, simulated collisions.

scholarly journals Strain gauge measurements on a full scale tidal turbine blade

2021 ◽  
Vol 170 ◽  
pp. 985-996
Author(s):  
Thomas Lake ◽  
Jack Hughes ◽  
Michael Togneri ◽  
Alison J. Williams ◽  
Penny Jeffcoate ◽  
...  
Keyword(s):  
Turbine Blade ◽  
Strain Gauge ◽  
Full Scale ◽  
Tidal Turbine ◽  
Strain Gauge Measurements

Fan Blade Flutter: Single Blade Instability or Blade to Blade Coupling?

1985 ◽  
Author(s):  
Edmond Széchényi
Keyword(s):  
Wind Tunnel ◽  
Flow Regimes ◽  
Single Degree Of Freedom ◽  
Single Degree ◽  
Different Types ◽  
Blade Flutter ◽  
Physical Insight ◽  
Fan Blade ◽  
Cascade Effects ◽  
Mode Order

Different types of fan blade flutter occur at the various compressor flow regimes. Sub/transonic stall flutter and two forms of supersonic started flow flutter have been studied in a straight cascade wind tunnel. Results show clearly that these three common forms of flutter can exist as single-degree-of-freedom (single-blade instabilities). Cascade effects, though at times important, are never the only flutter mechanism: flutter limits are essentially controlled by single-blade aeroelastic coefficients, though blade-to-blade coupling arising from cascade effects can modify these limits according to the mode order. Thus, contrary to widespread practice, the fundamental approach to flutter problems should lie at least as much in the study of single blade flutter as in that of unsteady cascade effects. The two should anyhow best be considered separately when searching for a better physical insight.

Methods of Studying the Effects of Blast Waves on Ships’ Superstructures

1969 ◽  
Vol 6 (03) ◽  
pp. 268-273
Author(s):  
John M. Dewey
Keyword(s):  
Shock Waves ◽  
Dynamic Response ◽  
Physical Properties ◽  
Blast Wave ◽  
Blast Waves ◽  
Full Scale ◽  
Single Degree Of Freedom ◽  
Structure Response ◽  
Single Degree ◽  
Interaction Of Shock Waves

Techniques are described which have been used to predict the possible effects of blast waves on ships' superstructures. The basic physical properties of a blast wave, the factors which affect these properties, and the techniques for measuring them are discussed. The interaction of shock waves with scaled rigid models is studied in the laboratory and the results are used to predict the blast loading on a full-scale structure. The dynamic response of the structure to this loading through the elastic, elasto-plastic, and plastic regimes can be calculated by reducing the structure to a system of simple single-degree-of-freedom components. These calculations are checked, when the opportunity arises, by studying the structure response on full-scale trials.

scholarly journals A cross-species neural integration of gravity for motor optimization

2021 ◽  
Vol 7 (15) ◽  
pp. eabf7800
Author(s):  
Jeremie Gaveau ◽  
Sidney Grospretre ◽  
Bastien Berret ◽  
Dora E. Angelaki ◽  
Charalambos Papaxanthis
Keyword(s):  
Optimization Strategy ◽  
Motor Patterns ◽  
Activation Patterns ◽  
Single Degree Of Freedom ◽  
Single Degree ◽  
Neural Integration ◽  
Gravity Effects ◽  
Neural Signature ◽  
Experimental Findings ◽  
Muscular Activation

Recent kinematic results, combined with model simulations, have provided support for the hypothesis that the human brain shapes motor patterns that use gravity effects to minimize muscle effort. Because many different muscular activation patterns can give rise to the same trajectory, here, we specifically investigate gravity-related movement properties by analyzing muscular activation patterns during single-degree-of-freedom arm movements in various directions. Using a well-known decomposition method of tonic and phasic electromyographic activities, we demonstrate that phasic electromyograms (EMGs) present systematic negative phases. This negativity reveals the optimal motor plan’s neural signature, where the motor system harvests the mechanical effects of gravity to accelerate downward and decelerate upward movements, thereby saving muscle effort. We compare experimental findings in humans to monkeys, generalizing the Effort-optimization strategy across species.

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