Flutter (electronics and communication)


Flutter (electronics and communication)

In the field of electronics and communication, "flutter" is the rapid variation of signal parameters, such as amplitude, phase, and 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 propagation, 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 absorption.
*In radio transmission, rapidly changing signal levels, together with variable multipath time delays, caused by reflection 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 circuit caused by the action of telegraph direct currents on the loading coils.
*In recording and reproducing equipment, the deviation of frequency caused by irregular mechanical motion, "e.g.," that of capstan angular velocity in a tape transport mechanism, during operation.

In the field of mechanics and structures, "flutter" refers to an aeroelastic phenomenon where a body's own aerodynamic forces couple with a 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 feedbackloop 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 67kph crosswind and became know as Galloping Gertie for its flutter movement.

During the 1950s over 100 incidences 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.

ee also

"Electronic Flutter"
* Wow (recording)
* Wow and flutter measurement

"Structural Flutter"
* Wind Engineering

References


Wikimedia Foundation. 2010.

Look at other dictionaries:

  • Flutter — can refer to: * Flutter on the iPhone * Flutter (electronics and communication), any rapid variation of signal parameters * Aeroelastic flutter, a rapid self excited motion, potentially destructive, in aircraft structures, control surfaces and… …   Wikipedia

  • Casete — de 60 minutos de la marca TDK. Características Codificación Señal analógica …   Wikipedia Español

  • Disco compacto — «CD» redirige aquí. Para otras acepciones, véase CD (desambiguación). Disco Compacto La superficie de lectura de un disco compacto incluye una pista en espiral con fuerza suficiente para causar que la luz difracte en el espectro visible completo …   Wikipedia Español

  • Microcasete — Microcassette de 60 minutos de la marca Maxell. Características Codificación Señal analógica …   Wikipedia Español

  • aerospace industry — Introduction       assemblage of manufacturing concerns that deal with vehicular flight within and beyond the Earth s atmosphere. (The term aerospace is derived from the words aeronautics and spaceflight.) The aerospace industry is engaged in the …   Universalium

  • Aerospace engineering — Aerospace Engineer NASA engineers, the ones depicted in the film Apollo 13, worked diligently to protect the lives of the astronauts on the mission. Occupation Names engineer aerospace engineer …   Wikipedia

  • Programmable logic controller — A programmable logic controller (PLC) or programmable controller is a digital computer used for automation of industrial processes, such as control of machinery on factory assembly lines. PLCs are used in many different industries and machines… …   Wikipedia

  • Boeing 787 Dreamliner — The first All Nippon Airways Boeing 787 (JA8 …   Wikipedia

  • Micropower — This article is about the technology pertaining to generating, storing or using extremely small amounts of power. For the British video game publisher, see Micro Power. Energy portal Micropower describes the work that researchers at several… …   Wikipedia

  • Merzbow discography — Masami Akita discography Releases ↙Studio albums 260 ↙Live albums 65 …   Wikipedia