|
Dynamic Instability
Dynamic instability may refer to any of several scientific phenomena: * Aircraft dynamic modes, including aircraft dynamic instability *Atmospheric instability, in meteorology * Dynamic instability of microtubules, in biology * Firehose instability, in astrophysics * Flutter, in aeroelasticity, a branch of mechanics *Hydrodynamic instability, in fluid dynamics *Speed wobble Speed wobble (also known as shimmy, tank-slapper, or death wobble) is a rapid side-to-side shaking of a vehicle's wheel(s) that occurs at high speeds and can lead to loss of control. It presents as a quick (4–10 Hz) oscillation of prim ..., in mechanical engineering **Others in :Fluid dynamic instabilities {{SIA ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Aircraft Dynamic Modes
The dynamic stability of an aircraft refers to how the aircraft behaves after it has been disturbed following steady non-oscillating flight. Longitudinal modes Oscillating motions can be described by two parameters, the period of time required for one complete oscillation, and the time required to damp to half-amplitude or the time to double the amplitude for a dynamically unstable motion. The longitudinal motion consists of two distinct oscillations, a long-period oscillation called a phugoid mode and a short-period oscillation referred to as the short-period mode. Phugoid (longer period) oscillations The longer period mode, called the "phugoid mode," is the one in which there is a large-amplitude variation of air-speed, pitch angle, and altitude, but almost no angle-of-attack variation. The phugoid oscillation is a slow interchange of kinetic energy (velocity) and potential energy (height) about some equilibrium energy level as the aircraft attempts to re-establish the equi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Atmospheric Instability
Atmospheric instability is a condition where the Earth's atmosphere is considered to be unstable and as a result local weather is highly variable through distance and time. Atmospheric instability encourages vertical motion, which is directly correlated to different types of weather systems and their severity. For example, under unstable conditions, a lifted air parcel, parcel of air will find cooler and denser surrounding air, making the parcel prone to further ascent, in a positive feedback loop. In meteorology, instability can be described by various indices such as the Bulk Richardson Number, lifted index, K-index (meteorology), K-index, convective available potential energy, convective available potential energy (CAPE), the Showalter, and the Vertical totals. These indices, as well as atmospheric instability itself, involve temperature changes through the troposphere with height, or lapse rate. Effects of atmospheric instability in moist atmospheres include thunderstorm d ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Microtubule
Microtubules are polymers of tubulin that form part of the cytoskeleton and provide structure and shape to eukaryotic cells. Microtubules can be as long as 50 micrometres, as wide as 23 to 27 nanometer, nm and have an inner diameter between 11 and 15 nm. They are formed by the polymerization of a Protein dimer, dimer of two globular proteins, Tubulin#Eukaryotic, alpha and beta tubulin into #Structure, protofilaments that can then associate laterally to form a hollow tube, the microtubule. The most common form of a microtubule consists of 13 protofilaments in the tubular arrangement. Microtubules play an important role in a number of cellular processes. They are involved in maintaining the structure of the cell and, together with microfilaments and intermediate filaments, they form the cytoskeleton. They also make up the internal structure of cilia and flagella. They provide platforms for intracellular transport and are involved in a variety of cellular processes, in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Firehose Instability
The firehose instability (or hose-pipe instability) is a dynamical instability of thin or elongated galaxies. The instability causes the galaxy to buckle or bend in a direction perpendicular to its long axis. After the instability has run its course, the galaxy is less elongated (i.e. rounder) than before. Any sufficiently thin stellar system, in which some component of the internal velocity is in the form of random or counter-streaming motions (as opposed to rotation), is subject to the instability. The firehose instability is probably responsible for the fact that elliptical galaxies and dark matter haloes never have axis ratios more extreme than about 3:1, since this is roughly the axis ratio at which the instability sets in. It may also play a role in the formation of barred spiral galaxies, by causing the bar to thicken in the direction perpendicular to the galaxy disk. The firehose instability derives its name from a similar instability in magnetized plasmas. However, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Aeroelasticity
Aeroelasticity is the branch of physics and engineering studying the interactions between the inertial, elastic, and aerodynamic forces occurring while an elastic body is exposed to a fluid flow. The study of aeroelasticity may be broadly classified into two fields: ''static aeroelasticity'' dealing with the static or steady state response of an elastic body to a fluid flow, and ''dynamic aeroelasticity'' dealing with the body's dynamic (typically vibrational) response. Aircraft are prone to aeroelastic effects because they need to be lightweight while enduring large aerodynamic loads. Aircraft are designed to avoid the following aeroelastic problems: # divergence where the aerodynamic forces increase the twist of a wing which further increases forces; # control reversal where control activation produces an opposite aerodynamic moment that reduces, or in extreme cases reverses, the control effectiveness; and # flutter which is uncontained vibration that can lead to the destr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hydrodynamic Instability
In fluid dynamics, hydrodynamic stability is the field which analyses the stability and the onset of instability of fluid flows. The study of hydrodynamic stability aims to find out if a given flow is stable or unstable, and if so, how these instabilities will cause the development of turbulence.See Drazin (2002), ''Introduction to hydrodynamic stability'' The foundations of hydrodynamic stability, both theoretical and experimental, were laid most notably by Helmholtz, Kelvin, Rayleigh and Reynolds during the nineteenth century. These foundations have given many useful tools to study hydrodynamic stability. These include Reynolds number, the Euler equations, and the Navier–Stokes equations. When studying flow stability it is useful to understand more simplistic systems, e.g. incompressible and inviscid fluids which can then be developed further onto more complex flows. Since the 1980s, more computational methods are being used to model and analyse the more complex flows. Stab ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Speed Wobble
Speed wobble (also known as shimmy, tank-slapper, or death wobble) is a rapid side-to-side shaking of a vehicle's wheel(s) that occurs at high speeds and can lead to loss of control. It presents as a quick (4–10 Hz) oscillation of primarily the steerable wheel(s), and is caused by a combination of factors, including initial disturbances and insufficient damping, which can create a resonance effect. Initially, the rest of the vehicle remains mostly unaffected, until translated into a vehicle yaw oscillation of increasing amplitude, producing loss of control. Vehicles that can experience this oscillation include motorcycles and bicycles, skateboards, and, in theory, any vehicle with a single steering pivot point and a sufficient amount of freedom of the steered wheel, including that which exists on some light aircraft with tricycle gear where instability can occur at speeds of less than ; this does not include most automobiles. The initial instability occurs mostly at h ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
