# FEDEM Offshore & Marine

FEDEM software including environmental structural loads from waves, currents and vessel dynamics.

FEDEM Offshore & Marine 7, built on FEDEM Mechanical 7, includes functionality for modeling and simulating structure interaction with sea water and soil, etc. FEDEM Offshore & Marine 7 has a large set of features particularly designed for oil & gas drilling risers and similar structures.

## Sea states

The sea state defines the sea environment properties, needed for calculation of hydrodynamic loads acting on the structure. It involves definition of waves and current as function of space and time. Properties for extra mass and drag due to marine growth on the structure is also provided in the sea state definition. Both regular and irregular waves, based on linear Airy wave theory is available, for finite and infinite (deep water) water depths. The irregular waves are based on the JONSWAP wave spectrum. Deterministic extreme waves based on 5th order Stokes theory or Streamline functions is also available.

## WATER-Structure Interaction

Hydrodynamic loads on slender beam structures are calculated based on the Morison equation, which yields added mass and drag forces due to the relative motion between the structure and water particles. In addition, buoyancy and possibly additional mass from internal fluids (mud) is accounted for.

## Soil-Structure Interaction

Soil piles are conveniently modelled as vertical beam structures with a set of nonlinear springs to ground at each FE node, giving a discrete representation of the soil interaction. The soil properties are specified as p-y and t-z curves at the different depth levels. The soil springs may also be assigned a cyclic hysteresis behaviour to model the plastification of the soil over a long and repetitive load history.

## Rig & Vessel Motion

A Response Amplitude Operator (RAO) is used to express the motion of a point on a rigid vessel floating in the sea as a function of the wave height at the same reference point. The concept of a RAOs is associated with the stationary sinusoidal response (or motion) of a linear system due to a stationary sinusoidal load (wave). The vessel motion amplutude is assumed to be proportional to the wave amplitude for a given frequency, but is normally not in phase with the wave.

## Riser Modelling

Flexible risers are modelled as a chain of beam elements (a beamstring) with circular and hollow cross sections. They are assigned drag and added mass coefficients for hydrodynamic load calculations. Internal mud may be defined, with a mass density different from the surrounding waters and with mud level independent from the mean sea level. A pipe-in-pipe contact may be set up through a tool that pairs two beamstrings together with a set of linear nor nonlinear springs in between to model the contact behaviour.

Please see the feature comparison for detailed features.