Slosh dynamics
Encyclopedia
In fluid dynamics
, slosh refers to the movement of liquid
inside another object (which is, typically, also undergoing motion). Strictly speaking, the liquid must have a free surface
to constitute a slosh dynamics problem, where the dynamics of the liquid can interact with the container to alter the system dynamics significantly. Important examples include propellant
slosh in spacecraft
tanks and rocket
s (especially upper stages), and 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".
Such motion is characterized by "inertial wave
s" and can be an important effect in spinning spacecraft dynamics. Extensive mathematical and empirical relationships have been derived to describe liquid slosh. These types of analyses are typically undertaken using computational fluid dynamics
and finite element methods to solve the fluid-structure interaction
problem, especially if the solid container is flexible. Relevant fluid dynamics non-dimensional parameters include the Bond number, the Weber number
, and the Reynolds number.
Slosh is an important effect for spacecraft, ships, and some aircraft
. Slosh was a factor in the recent Falcon 1
second test flight anomaly, and has been implicated in various other spacecraft anomalies, including a near-disaster with the Near Earth Asteroid Rendezvous (NEAR Shoemaker
) satellite.
which can alter the shape (and thus the eigenvalues) of the liquid slug. Typically, a large part of the mass fraction 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 called jitter
. Similar phenomena can cause pogo oscillation
and can result in structural failure of space vehicle.
Another example is problematic interaction with the spacecraft Attitude Control System (ACS), especially for spinning satellites which can suffer resonance
between slosh and nutation
, or adverse changes to the rotational inertia
. Because of these types of risk
, in the 1960s the National Aeronautics and Space Administration (NASA) extensively studied liquid slosh in spacecraft tanks, and in the 1990s NASA undertook the Middeck 0-Gravity Dynamics Experiment on the space shuttle
. The European Space Agency
has advanced these investigations with the launch of SLOSHSAT. Most spinning spacecraft since 1980 have been tested at the Applied Dynamics Laboratories drop tower using sub-scale models. Extensive contributions have also been made by the Southwest Research Institute
, but research is widespread in academia and industry.
Research is continuing into slosh effects on in-space
propellant depot
s. In October 2009, the Air Force and United Launch Alliance
(ULA) performed an experimental on-orbit demonstration on a modified Centaur upper stage on the DMSP-18 satellite launch in order to improve "understanding of propellant settling and slosh." "The light weight of DMSP-18 allowed 12000 lbs 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 planned deorbit burn was executed.
ULA has additional small-scale demonstrations of cryogenic fluid management are planned with project CRYOTE in 2012-2014
leading to a ULA large-scale cryo-sat propellant depot test under the NASA flagship technology demonstration program in 2015.
, water ballast
, or other liquid (e.g. from leaks or fire fighting) can cause disastrous capsizing
in ships due to free surface effect
; this can also affect trucks and aircraft.
The effect of slosh is used to limit the bounce of a roller hockey
ball. Water slosh can significantly reduce the rebound height of a ball but some amounts of liquid seem to lead to a resonance
effect. Many of the balls for roller hockey commonly available contain water to reduce the bounce height.
Fluid dynamics
In physics, fluid dynamics is a sub-discipline of fluid mechanics that deals with fluid flow—the natural science of fluids in motion. It has several subdisciplines itself, including aerodynamics and hydrodynamics...
, slosh refers to the movement of liquid
Liquid
Liquid is one of the three classical states of matter . Like a gas, a liquid is able to flow and take the shape of a container. Some liquids resist compression, while others can be compressed. Unlike a gas, a liquid does not disperse to fill every space of a container, and maintains a fairly...
inside another object (which is, typically, also undergoing motion). Strictly speaking, the liquid must have a free surface
Free surface
In physics, a free surface is the surface of a fluid that is subject to constant perpendicular normal stress and zero parallel shear stress,such as the boundary between two homogenous fluids,for example liquid water and the air in the Earth's atmosphere...
to constitute a slosh dynamics problem, where the dynamics of the liquid can interact with the container to alter the system dynamics significantly. Important examples include propellant
Propellant
A propellant is a material that produces pressurized gas that:* can be directed through a nozzle, thereby producing thrust ;...
slosh in spacecraft
Spacecraft
A spacecraft or spaceship is a craft or machine designed for spaceflight. Spacecraft are used for a variety of purposes, including communications, earth observation, meteorology, navigation, planetary exploration and transportation of humans and cargo....
tanks and rocket
Rocket
A rocket is a missile, spacecraft, aircraft or other vehicle which obtains thrust from a rocket engine. In all rockets, the exhaust is formed entirely from propellants carried within the rocket before use. Rocket engines work by action and reaction...
s (especially upper stages), and cargo slosh
Free Surface Effect
The free surface effect is one of several mechanisms which can cause a craft to become unstable and roll over . It refers to the tendency of liquids — and of aggregates of small solid objects, like seeds, gravel, or crushed ore which can act as liquids — to slosh about: to move in response to...
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".
Such motion is characterized by "inertial wave
Inertial wave
Inertial waves, also known as inertial oscillations, are a type of mechanical wave possible in rotating fluids. Unlike surface gravity waves commonly seen at the beach or in the bathtub, inertial waves travel through the interior of the fluid, not at the surface...
s" and can be an important effect in spinning spacecraft dynamics. Extensive mathematical and empirical relationships have been derived to describe liquid slosh. These types of analyses are typically undertaken using 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...
and finite element methods to solve the fluid-structure interaction
Fluid-Structure Interaction
Fluid-structure interaction is the interaction of some movable or deformable structure with an internal or surrounding fluid flow. Fluid-structure interactions can be stable or oscillatory...
problem, especially if the solid container is flexible. Relevant fluid dynamics non-dimensional parameters include the Bond number, the Weber number
Weber number
The Weber number is a dimensionless number in fluid mechanics that is often useful in analysing fluid flows where there is an interface between two different fluids, especially for multiphase flows with strongly curved surfaces. It can be thought of as a measure of the relative importance of the...
, and the Reynolds number.
Slosh is an important effect for spacecraft, ships, and some aircraft
Aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...
. Slosh was a factor in the recent Falcon 1
Falcon 1
The Falcon 1 is a partially reusable launch system designed and manufactured by SpaceX, a space transportation company in Hawthorne, California. The two-stage-to-orbit rocket uses LOX/RP-1 for both stages, the first powered by a single Merlin engine and the second powered by a single Kestrel engine...
second test flight anomaly, and has been implicated in various other spacecraft anomalies, including a near-disaster with the Near Earth Asteroid Rendezvous (NEAR Shoemaker
NEAR Shoemaker
The Near Earth Asteroid Rendezvous - Shoemaker , renamed after its 1996 launch in honor of planetary scientist Eugene M. Shoemaker, was a robotic space probe designed by the Johns Hopkins University Applied Physics Laboratory for NASA to study the near-Earth asteroid Eros from close orbit over a...
) satellite.
Spacecraft effects
Liquid slosh in microgravity is relevant to spacecraft, most commonly Earth-orbiting satellites, and must take account of liquid surface tensionSurface tension
Surface tension is a property of the surface of a liquid that allows it to resist an external force. It is revealed, for example, in floating of some objects on the surface of water, even though they are denser than water, and in the ability of some insects to run on the water surface...
which can alter the shape (and thus the eigenvalues) of the liquid slug. Typically, a large part of the mass fraction 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 called jitter
Jitter
Jitter is the undesired deviation from true periodicity of an assumed periodic signal in electronics and telecommunications, often in relation to a reference clock source. Jitter may be observed in characteristics such as the frequency of successive pulses, the signal amplitude, or phase of...
. Similar phenomena can cause pogo oscillation
Pogo oscillation
Pogo oscillation is a potentially dangerous type of self-excited combustion oscillation in liquid fuel rocket engines. This oscillation results in variations of thrust from the engines, causing variations of acceleration on the rocket's structure, giving variations in fuel pressure and flow rate....
and can result in structural failure of space vehicle.
Another example is problematic interaction with the spacecraft Attitude Control System (ACS), especially for spinning satellites which can suffer resonance
Resonance
In physics, resonance is the tendency of a system to oscillate at a greater amplitude at some frequencies than at others. These are known as the system's resonant frequencies...
between slosh and nutation
Nutation
Nutation is a rocking, swaying, or nodding motion in the axis of rotation of a largely axially symmetric object, such as a gyroscope, planet, or bullet in flight, or as an intended behavior of a mechanism...
, or adverse changes to the rotational inertia
Inertia
Inertia is the resistance of any physical object to a change in its state of motion or rest, or the tendency of an object to resist any change in its motion. It is proportional to an object's mass. The principle of inertia is one of the fundamental principles of classical physics which are used to...
. Because of these types of risk
Risk
Risk is the potential that a chosen action or activity will lead to a loss . The notion implies that a choice having an influence on the outcome exists . Potential losses themselves may also be called "risks"...
, in the 1960s the National Aeronautics and Space Administration (NASA) extensively studied liquid slosh in spacecraft tanks, and in the 1990s NASA undertook the Middeck 0-Gravity Dynamics Experiment on the space shuttle
Space Shuttle
The Space Shuttle was a manned orbital rocket and spacecraft system operated by NASA on 135 missions from 1981 to 2011. The system combined rocket launch, orbital spacecraft, and re-entry spaceplane with modular add-ons...
. The European Space Agency
European Space Agency
The European Space Agency , established in 1975, is an intergovernmental organisation dedicated to the exploration of space, currently with 18 member states...
has advanced these investigations with the launch of SLOSHSAT. Most spinning spacecraft since 1980 have been tested at the Applied Dynamics Laboratories drop tower using sub-scale models. Extensive contributions have also been made by the Southwest Research Institute
Southwest Research Institute
Southwest Research Institute , headquartered in San Antonio, Texas, is one of the oldest and largest independent, nonprofit, applied research and development organizations in the United States...
, but research is widespread in academia and industry.
Research is continuing into slosh effects on in-space
Outer space
Outer space is the void that exists between celestial bodies, including the Earth. It is not completely empty, but consists of a hard vacuum containing a low density of particles: predominantly a plasma of hydrogen and helium, as well as electromagnetic radiation, magnetic fields, and neutrinos....
propellant depot
Propellant depot
An orbital propellant depot is a cache of propellant that is placed on an orbit about the Earth or another body to allow spacecraft to be fuelled in space. Launching a spacecraft separately from some of its propellant enables missions with more massive payloads...
s. In October 2009, the Air Force and United Launch Alliance
United Launch Alliance
United Launch Alliance is a joint venture of Lockheed Martin and Boeing. ULA was formed in December 2006 by combining the teams at these companies which provide spacecraft launch services to the government of the United States. U.S...
(ULA) performed an experimental on-orbit demonstration on a modified Centaur upper stage on the DMSP-18 satellite launch in order to improve "understanding of propellant settling and slosh." "The light weight of DMSP-18 allowed 12000 lbs 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 planned deorbit burn was executed.
ULA has additional small-scale demonstrations of cryogenic fluid management are planned with project CRYOTE in 2012-2014
leading to a ULA large-scale cryo-sat propellant depot test under the NASA flagship technology demonstration program in 2015.
Practical effects
Sloshing or shifting cargoCargo
Cargo is goods or produce transported, generally for commercial gain, by ship, aircraft, train, van or truck. In modern times, containers are used in most intermodal long-haul cargo transport.-Marine:...
, water ballast
Sailing ballast
Ballast is used in sailboats to provide moment to resist the lateral forces on the sail. Insufficiently ballasted boats will tend to tip, or heel, excessively in high winds. Too much heel may result in the boat capsizing. If a sailing vessel should need to voyage without cargo then ballast of...
, or other liquid (e.g. from leaks or fire fighting) can cause disastrous capsizing
Capsize
Capsizing is an act of tipping over a boat or ship to disable it. The act of reversing a capsized vessel is called righting.If a capsized vessel has sufficient flotation to prevent sinking, it may recover on its own if the stability is such that it is not stable inverted...
in ships due to free surface effect
Free Surface Effect
The free surface effect is one of several mechanisms which can cause a craft to become unstable and roll over . It refers to the tendency of liquids — and of aggregates of small solid objects, like seeds, gravel, or crushed ore which can act as liquids — to slosh about: to move in response to...
; this can also affect trucks and aircraft.
The effect of slosh is used to limit the bounce of a roller hockey
Roller hockey
Roller Hockey is a form of hockey played on a dry surface using skates with wheels. The term "Roller Hockey" is often used interchangeably to refer to two variant forms chiefly differentiated by the type of skate used. There is traditional "Roller Hockey," played with quad roller skates, and...
ball. Water slosh can significantly reduce the rebound height of a ball but some amounts of liquid seem to lead to a resonance
Resonance
In physics, resonance is the tendency of a system to oscillate at a greater amplitude at some frequencies than at others. These are known as the system's resonant frequencies...
effect. Many of the balls for roller hockey commonly available contain water to reduce the bounce height.
See also
- Free surface effectFree Surface EffectThe free surface effect is one of several mechanisms which can cause a craft to become unstable and roll over . It refers to the tendency of liquids — and of aggregates of small solid objects, like seeds, gravel, or crushed ore which can act as liquids — to slosh about: to move in response to...
- Splash (fluid mechanics)Splash (fluid mechanics)In fluid mechanics, a splash is a sudden disturbance to the otherwise quiescent free surface of a liquid . The disturbance is typically caused by a solid object suddenly hitting the surface, although splashes can occur in which moving liquid supplies the energy...
, other free surface phenomena - Succussion splashSuccussion splashSuccussion splash is a sloshing sound heard through the stethoscope during sudden movement of the patient on abdominal auscultation. It reflects the presence of gas and fluid in an obstructed organ, as in gastric outlet obstruction.-References:...
, audible medical sign