The RELAP5-3D code is typically used to model stationary, land-based, thermal-hydraulic systems and contains specialized physics for the modeling of nuclear power plants. It can also model thermal-hydraulic systems in other inertial and accelerating frames of reference. By changing the magnitude of the gravitational vector through user input, RELAP5-3D can model thermal-hydraulic systems on planets, moons, and space stations. Additionally, the field equations were modified to model thermal-hydraulic systems in a noninertial frame, such as occur onboard moving craft or during earthquakes for land-based systems.

Transient body forces affect fluid flow in thermal-fluid machinery aboard accelerating crafts during rotational and translational accelerations. It is useful to express the equations of fluid motion in the accelerating frame of reference attached to the moving craft. However, careful treatment of the rotational and translational kinematics is required to accurately capture the physics of fluid motion. Correlations for flow at angles between horizontal and vertical are generated via interpolation because limited experimental data exist.

Equations for three-dimensional fluid motion in a noninertial frame of reference are developed. Two different systems for describing rotational motion are presented, user input is discussed, and examples of a modeled simple thermal-hydraulic system undergoing both rotational and translational motion are provided.