Influid 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.[1] Important examples include propellant slosh in spacecraft tanks and rockets (especially upper stages), and cargo slosh in ships and trucks transporting liquids (for example oil and gasoline): see free surface effect.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 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 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,[4] 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[5] with the Near Earth Asteroid Rendezvous (NEAR Shoemaker) satellite.
Liquid slosh in microgravity[6][7] is relevant to spacecraft, most commonly Earth-orbiting satellites, and must take account of liquid surface tension 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 impact satellite performance in a number of ways. For example, propellant slosh can introduce uncertainty in spacecraft attitude (pointing) which is often called jitter. Similar phenomenon 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[8] 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[9] liquid slosh in spacecraft tanks, and in the 1990s NASA undertook the Middeck 0-Gravity Dynamics Experiment[10] on the space shuttle. The European Space Agency has advanced these investigations[11][12][13][14] with the launch of SLOSHSAT. Extensive contributions have also been made[15] by the Southwest Research Institute, but research is widespread[16] in academia and industry.
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[17] 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.
