Influid dynamics,slosh refers to the movement ofliquid inside another object (which is, typically, also undergoing motion).
Strictly speaking, the liquid must have afree surface to constitute aslosh dynamics problem, where the dynamics of the liquid can interact with the container to alter the system dynamics significantly.[1] Important examples includepropellant slosh inspacecraft tanks androckets (especially upper stages), and thefree surface effect (cargo slosh) in ships and trucks transporting liquids (for example oil and gasoline).However, it has become common to refer to liquid motion in a completely filled tank, i.e. without a free surface, as "fuel slosh".[not verified in body]
Such motion is characterized by "inertial waves" and can be an important effect in spinning spacecraft dynamics. Extensive mathematical and empirical relationships have been derived to describe liquid slosh.[2][3] These types of analyses are typically undertaken usingcomputational fluid dynamics andfinite element methods to solve thefluid-structure interaction problem, especially if the solid container is flexible. Relevant fluid dynamics non-dimensional parameters include theBond number, theWeber number, and theReynolds number.
Slosh is an important effect for spacecraft,[4] ships,[3] some land vehicles and someaircraft. Slosh was a factor in theFalcon 1 second test flight anomaly, and has been implicated in various other spacecraft anomalies, including a near-disaster[5] with the Near Earth Asteroid Rendezvous (NEAR Shoemaker) satellite.
Liquid slosh inmicrogravity[6][7] is relevant to spacecraft, most commonly Earth-orbitingsatellites, and must take account of liquidsurface tension which can alter the shape (and thus theeigenvalues) of the liquid slug. Typically, a large fraction of the mass of a satellite is liquid propellant at/near Beginning of Life (BOL), and slosh can adversely affect satellite performance in a number of ways. For example, propellant slosh can introduce uncertainty in spacecraft attitude (pointing) which is often calledjitter. Similar phenomena can causepogo oscillation and can result in structural failure of a space vehicle.
Another example is problematic interaction with the spacecraft's Attitude Control System (ACS), especially for spinning satellites[8] which can sufferresonance between slosh andnutation, or adverse changes to the rotationalinertia. Because of these types ofrisk, in the 1960s theNational Aeronautics and Space Administration (NASA) extensively studied[9] liquid slosh in spacecraft tanks, and in the 1990s NASA undertook theMiddeck 0-Gravity Dynamics Experiment[10] on theSpace Shuttle. TheEuropean Space Agency has advanced these investigations[11][12][13][14] with the launch ofSLOSHSAT. Most spinning spacecraft since 1980 have been tested at the Applied Dynamics Laboratories drop tower using sub-scale models.[15] Extensive contributions have also been made[16] by theSouthwest Research Institute, but research is widespread[17] in academia and industry.
Research is continuing into slosh effects on in-spacepropellant depots. In October 2009, theUnited States Air Force andUnited Launch Alliance (ULA) performed an experimentalon-orbit demonstration on a modifiedCentaur upper stage on theDMSP-18 satellitelaunch in order to improve "understanding ofpropellant settling and slosh", "The light weight of DMSP-18 allowed 12,000 pounds (5,400 kg) of remaining LO2 and LH2 propellant, 28% of Centaur’s capacity", for the on-orbit tests. The post-spacecraft mission extension ran 2.4 hours before the planneddeorbit burn was executed.[18]
NASA'sLaunch Services Program is working on two on-goingslosh fluid dynamics experiments with partners:CRYOTE andSPHERES-Slosh.[19] ULA has additional small-scale demonstrations of cryogenic fluid management are planned with project CRYOTE in 2012–2014[20] leading to a ULA large-scale cryo-sat propellant depot test under the NASAflagship technology demonstrations program in 2015.[20] SPHERES-Slosh withFlorida Institute of Technology andMassachusetts Institute of Technology will examine how liquids move around inside containers in microgravity with the SPHERES Testbed on theInternational Space Station.
Liquid sloshing strongly influences the directional dynamics and safety performance of highwaytank vehicles in a highly adverse manner.[21] Hydrodynamicforces andmoments arising from liquidcargo oscillations in the tank understeering and/orbraking maneuvers reduce the stability limit and controllability of partially-filledtank vehicles.[22][23][24] Anti-slosh devices such as baffles are widely used in order to limit the adverse liquid slosh effect on directional performance and stability of thetank vehicles.[25] Since most of the time, tankers are carrying dangerous liquid contents such as ammonia, gasoline and fuel oils, stability of partially-filled liquid cargo vehicles is very important. Optimizations and sloshing reduction techniques in fuel tanks such as elliptical tank, rectangular, modified oval and generic tank shape have been performed in different filling levels using numerical, analytical and analogical analyses. Most of these studies concentrate on effects of baffles on sloshing while the influence of cross-section is completely ignored.[26]
TheBloodhound LSR 1,000 mph project car utilizes a liquid-fuelled rocket that requires a specially-baffled oxidizer tank to prevent directional instability, rocket thrust variations and even oxidizer tank damage.[27]
Sloshing or shiftingcargo, waterballast, or other liquid (e.g., from leaks or fire fighting) can cause disastrouscapsizing in ships due tofree surface effect; this can also affect trucks and aircraft.
The effect of slosh is used to limit the bounce of aroller hockey ball. Water slosh can significantly reduce the rebound height of a ball[28] but some amounts of liquid seem to lead to aresonance effect. Many of the balls for roller hockey commonly available contain water to reduce the bounce height.