Quadratic Mode Shape Components From Ground Vibration Testing

2012 ◽  
Vol 134 (3) ◽  
Author(s):  
L. H. van Zyl ◽  
E. H. Mathews
Keyword(s):  
Mode Shape ◽  
Ground Vibration ◽  
Axial Displacement ◽  
Vibration Test ◽  
Transverse Displacement ◽  
Vibration Testing ◽  
Linear Mode ◽  
Quadratic Mode ◽  
Acceleration Signals ◽  
Shape Component

Points on a vibrating structure generally move along curved paths rather than straight lines. For example, the tip of a cantilever beam vibrating in a bending mode experiences axial displacement as well as transverse displacement. The axial displacement is governed by the inextensibility of the neutral axis of the beam and is proportional to the square of the transverse displacement; hence the name “quadratic mode shape component.” Quadratic mode shape components are largely ignored in modal analysis, but there are some applications in the field of modal-basis structural analysis where the curved path of motion cannot be ignored. Examples include vibrations of rotating structures and buckling. Methods employing finite element analysis have been developed to calculate quadratic mode shape components. Ground vibration testing typically only yields the linear mode shape components. This paper explores the possibility of measuring the quadratic mode shape components in a sine-dwell ground vibration test. This is purely an additional measurement and does not affect the measured linear mode shape components or the modal parameters, i.e., modal mass, frequency, and damping ratio. The accelerometer output was modeled in detail taking into account its linear acceleration, its rotation, and gravitational acceleration. The response was correlated with the Fourier series representation of the output signal. The result was a simple expression for the quadratic mode shape component. The method was tested on a simple test piece and satisfactory results were obtained. The method requires that the accelerometers measure down to steady state and that up to the second Fourier coefficients of the output signals are calculated. The proposed method for measuring quadratic mode shape components in a sine-dwell ground vibration test seems feasible. One drawback of the method is that it is based on the measurement and processing of second harmonics in the acceleration signals and is therefore sensitive to any form of structural nonlinearity that may also cause higher harmonics in the acceleration signals. Another drawback is that only the quadratic components of individual modes can be measured, whereas coupled quadratic terms are generally also required to fully describe the motion of a point on a vibrating structure.

Ground vibration testing of a helicopter rotor blade using optical fibre sensors

2019 ◽  
Author(s):  
Thomas Kissinger ◽  
Simone Weber ◽  
Edmond Chehura ◽  
James H. Barrington ◽  
Stephen Staines ◽  
...  
Keyword(s):  
Optical Fibre ◽  
Rotor Blade ◽  
Ground Vibration ◽  
Helicopter Rotor ◽  
Vibration Testing ◽  
Optical Fibre Sensors ◽  
Helicopter Rotor Blade

scholarly journals Technology of Ground Vibration Testing and its application in light aircraft prototyping

2019 ◽  
Vol 304 ◽  
pp. 01005
Author(s):  
Aleksander Olejnik ◽  
Stanisław Kachel ◽  
Robert Rogólski ◽  
Michał Szcześniak
Keyword(s):  
Early Stage ◽  
Ground Vibration ◽  
Measuring System ◽  
Vibration Measurement ◽  
Measurement Technology ◽  
Vibration Testing ◽  
Resonant Frequencies ◽  
Natural Modes ◽  
University Of Technology ◽  
The Military

The article describes the vibration measurement technology used for light aircraft and some results obtained during the prototyping process. The aim of researches was to determine the resonant frequencies and natural modes of an aircraft or its selected structural components. Ground Vibration Testing is an essential dynamic structural test necessary to carry out before the aircraft certification. This test should be performed on the aircraft example which is predicted to test in flight. The measuring system used in the Institute of Aviation Technology of the Military University of Technology consists of a multi-channel LMS SCADAS analyzer, a set of piezoelectric accelerometers, two vibration exciters equipped with impedance heads and a computer with the Test.Lab Software. The aim of the article is to present the methodology of performing GVT tests. Using the equipment applied to an aircraft or its airframe component, key vibration characteristics corresponding to resonant points can be determined. Not only completed aircraft can be tested, but also its isolated fragments (wings, stabilizers, tail units) or just empty airframe. Testing separately supported components allows to examine their aeroelastic properties at early stage of prototyping. As examples of the use of vibration measurements in various stages of the prototyping process, three examples are presented herein. The isolated strut-braced wing from of the light reconnaissance aircraft OSA, the airframe of a light jet FLARIS LAR, and the light drone ATD JET-2 intended to be an aerial target for some anti-aircraft artillery sets. Some exemplary results obtained from testing these objects were presented. At the end, some observations and conclusions were noted in the context of usefulness of conducted researches.

Application of ground vibration testing in small manned or unmanned aircraft prototyping

2020 ◽  
pp. 095441002093401
Author(s):  
Aleksander Olejnik ◽  
Stanisław Kachel ◽  
Robert Rogólski ◽  
Michał Szcześniak
Keyword(s):  
Early Stage ◽  
Ground Vibration ◽  
Unmanned Aircraft ◽  
Measuring System ◽  
Vibration Measurement ◽  
Measurement Technology ◽  
Vibration Testing ◽  
University Of Technology ◽  
Testing Technology ◽  
The Military

The article describes the vibration measurement technology used in experimental investigation of light aircraft and some series of exemplary results obtained during the prototyping process. The aim of investigations presented herein was to determine the resonant frequencies and natural modes of an aircraft or its selected structural components. Ground vibration testing is an essential dynamic structural test necessary to carry out before the aircraft certification. This test should be performed on the aircraft example which is predicted to be tested in flight. The measuring system used for ground vibration testing in the Institute of Aviation Technology of the Military University of Technology consists of a multi-channel LMS SCADAS analyzer, a set of piezoelectric accelerometers, two vibration exciters equipped with impedance heads and a computer with the Test.Lab Software. The aim of the article was to present the methodology of performing ground vibration testing tests. Having applied the equipment to measure an airplane or its airframe component, key vibration characteristics corresponding to specific resonant points can be determined. Not only completed aircraft can be tested but also its isolated fragments (wings, stabilizers, tail units) or just empty airframe. Testing separately supported components allows examining their aeroelastic properties at early stage of prototyping. Ground vibration testing technology applied in various stages of the prototyping process was demonstrated in four peculiar research cases. The testing examples presented herein were the following: the isolated strut-braced wing of a light reconnaissance airplane, the light drone imitating an aerial target for some on-ground anti-aircraft artillery sets, the empty airframe of a very light jet and the miniature UAV. Some exemplary results obtained from testing these objects were presented. At the end, some observations and conclusions were noted in the context of usefulness of conducted researches.

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