Flutter
Encyclopedia
In electronics
and communication
, flutter is the rapid variation
of signal parameters, such as amplitude
, phase
, and frequency
. Examples of electronic flutter are:
and structures, Aeroelastic flutter is an aeroelastic
phenomenon where a body's own aerodynamic forces couple with its natural mode of vibration
to produce rapid periodic motion.
Aeroelastic flutter occurs under steady flow conditions, when a structure's aerodynamic forces are affected by and in turn affect the movement of the structure. This sets up a positive feedback
loop exciting the structure's free vibration. Flutter is self-starting and results in large amplitude vibration which often lead to rapid failure.
The aerodynamic conditions required for flutter vary with the structure's external design and flexibility, but can range from very low velocities to supersonic flows. Large or flexible structures such as pipes, suspension bridges, chimneys and tall buildings are prone to flutter. Designing to avoid flutter is a fundamental requirement for rigid airfoils (fixed wing aircraft and helicopters) as well as for aircraft propellers and gas turbine blades.
Prediction of flutter prior to modern unsteady computational fluid dynamics
was based on empirical testing. As a result many pioneering designs failed due to unforeseen vibrations. The most famous of these was the opening of the original Tacoma Narrows Suspension Bridge
in mid 1940, which failed spectacularly 4 months later during a sustained 67 km/h crosswind and became known as Galloping Gertie for its flutter movement.
During the 1950s over 100 incidents were recorded of military or civilian aircraft being lost or damaged due to unforeseen flutter events. While as recently as the 1990s jet engine flutter has grounded military aircraft.
Techniques to avoid flutter include changes to the structure's aerodynamics, stiffening the structure to change the excitation frequency and increasing the damping
within the structure.
Structural Flutter
Electronics
Electronics is the branch of science, engineering and technology that deals with electrical circuits involving active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies...
and communication
Communication
Communication is the activity of conveying meaningful information. Communication requires a sender, a message, and an intended recipient, although the receiver need not be present or aware of the sender's intent to communicate at the time of communication; thus communication can occur across vast...
, flutter is the rapid variation
Variation
- Physics :* Magnetic variation, difference between magnetic north and true north, measured as an angle* Variation , any perturbation of the mean motion or orbit of a planet or satellite, particularly of the moon- Mathematics :* Bounded variation...
of signal parameters, such as amplitude
Amplitude
Amplitude is the magnitude of change in the oscillating variable with each oscillation within an oscillating system. For example, sound waves in air are oscillations in atmospheric pressure and their amplitudes are proportional to the change in pressure during one oscillation...
, phase
Phase (waves)
Phase in waves is the fraction of a wave cycle which has elapsed relative to an arbitrary point.-Formula:The phase of an oscillation or wave refers to a sinusoidal function such as the following:...
, and frequency
Frequency
Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...
. Examples of electronic flutter are:
- Rapid variations in received signal levels, such as variations that may be caused by atmospheric disturbances, antenna movements in a high wind, or interaction with other signals.
- In radio propagationRadio propagationRadio propagation is the behavior of radio waves when they are transmitted, or propagated from one point on the Earth to another, or into various parts of the atmosphere...
, a phenomenon in which nearly all radio signals that are usually reflected by ionospheric layers in or above the E-region experience partial or complete absorptionAbsorption (electromagnetic radiation)In physics, absorption of electromagnetic radiation is the way by which the energy of a photon is taken up by matter, typically the electrons of an atom. Thus, the electromagnetic energy is transformed to other forms of energy for example, to heat. The absorption of light during wave propagation is...
. - In radio transmissionTransmission (telecommunications)Transmission, in telecommunications, is the process of sending, propagating and receiving an analogue or digital information signal over a physical point-to-point or point-to-multipoint transmission medium, either wired, optical fiber or wireless...
, rapidly changing signal levels, together with variable multipath time delays, caused by reflectionReflection (physics)Reflection is the change in direction of a wavefront at an interface between two differentmedia so that the wavefront returns into the medium from which it originated. Common examples include the reflection of light, sound and water waves...
and possible partial absorption of the signal by aircraft flying through the radio beam or common scatter volume. - The variation in the transmission characteristics of a loaded telephone lineTelephone lineA telephone line or telephone circuit is a single-user circuit on a telephone communication system...
caused by the action of telegraph direct currents on the loadingLoadingIn electrical transmission lines, the term loading means the insertion of impedance into a circuit to change the characteristics of the circuit....
coils. - In recording and reproducing equipment, the deviation of frequencyFrequencyFrequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...
caused by irregular mechanical motion, e.g., that of capstan angular velocity in a tape transport mechanism, during operation.
Aeroelastic
In the field of mechanicsMechanics
Mechanics is the branch of physics concerned with the behavior of physical bodies when subjected to forces or displacements, and the subsequent effects of the bodies on their environment....
and structures, Aeroelastic flutter is an aeroelastic
Aeroelasticity
Aeroelasticity is the science which studies the interactions among inertial, elastic, and aerodynamic forces. It was defined by Arthur Collar in 1947 as "the study of the mutual interaction that takes place within the triangle of the inertial, elastic, and aerodynamic forces acting on structural...
phenomenon where a body's own aerodynamic forces couple with its natural mode of vibration
Vibration
Vibration refers to mechanical oscillations about an equilibrium point. The oscillations may be periodic such as the motion of a pendulum or random such as the movement of a tire on a gravel road.Vibration is occasionally "desirable"...
to produce rapid periodic motion.
Aeroelastic flutter occurs under steady flow conditions, when a structure's aerodynamic forces are affected by and in turn affect the movement of the structure. This sets up a positive feedback
Positive feedback
Positive feedback is a process in which the effects of a small disturbance on a system include an increase in the magnitude of the perturbation. That is, A produces more of B which in turn produces more of A. In contrast, a system that responds to a perturbation in a way that reduces its effect is...
loop exciting the structure's free vibration. Flutter is self-starting and results in large amplitude vibration which often lead to rapid failure.
The aerodynamic conditions required for flutter vary with the structure's external design and flexibility, but can range from very low velocities to supersonic flows. Large or flexible structures such as pipes, suspension bridges, chimneys and tall buildings are prone to flutter. Designing to avoid flutter is a fundamental requirement for rigid airfoils (fixed wing aircraft and helicopters) as well as for aircraft propellers and gas turbine blades.
Prediction of flutter prior to modern unsteady computational fluid dynamics
Computational fluid dynamics
Computational fluid dynamics, usually abbreviated as CFD, is a branch of fluid mechanics that uses numerical methods and algorithms to solve and analyze problems that involve fluid flows. Computers are used to perform the calculations required to simulate the interaction of liquids and gases with...
was based on empirical testing. As a result many pioneering designs failed due to unforeseen vibrations. The most famous of these was the opening of the original Tacoma Narrows Suspension Bridge
Tacoma Narrows Bridge (1940)
The 1940 Tacoma Narrows Bridge was the first incarnation of the Tacoma Narrows Bridge, a suspension bridge in the U.S. state of Washington that spanned the Tacoma Narrows strait of Puget Sound between Tacoma and the Kitsap Peninsula. It opened to traffic on July 1, 1940, and dramatically collapsed...
in mid 1940, which failed spectacularly 4 months later during a sustained 67 km/h crosswind and became known as Galloping Gertie for its flutter movement.
During the 1950s over 100 incidents were recorded of military or civilian aircraft being lost or damaged due to unforeseen flutter events. While as recently as the 1990s jet engine flutter has grounded military aircraft.
Techniques to avoid flutter include changes to the structure's aerodynamics, stiffening the structure to change the excitation frequency and increasing the damping
Damping
In physics, damping is any effect that tends to reduce the amplitude of oscillations in an oscillatory system, particularly the harmonic oscillator.In mechanics, friction is one such damping effect...
within the structure.
See also
Electronic Flutter- Wow (recording)Wow (recording)Wow is a relatively slow form of flutter which can affect both gramophone records and tape recorders. In the latter, the collective expression wow and flutter is commonly used.-Gramophone records:...
- Wow and flutter measurementWow and flutter measurementWow and flutter measurement is carried out on audio tape machines, cassette recorders and players, and other analog recording and reproduction devices with rotary components This measurement quantifies the amount of 'frequency wobble' present in subjectively valid terms...
Structural Flutter
- Wind EngineeringWind engineeringWind engineering analyzes effects of wind in the natural and the built environment and studies the possible damage, inconvenience or benefits which may result from wind. In the field of structural engineering it includes strong winds, which may cause discomfort, as well as extreme winds, such as in...