How to setup the warmup period in OpenFlows FLOOD coastal engine

This article will cover the necessary steps to setup warmup period for several types of forcings using the coastal hydrodynamic engine in OpenFlows FLOOD. 

Problem

By default, the coastal hydrodynamics engine MOHID Water that runs with OpenFlows FLOOD considers as initial solution null water level gradients and null velocities, i.e. the water in not moving at the start of the simulation and the water level is the same in the entire computational domain. When the simulation starts, boundary conditions and forcing functions are applied and the model computes a dynamic solution. Because the initial condition is normally not realistic (as coastal waters are always moving) during the initial stages of the simulation the solution maybe result in apparent numerical instability or "noise" and overall unreallistical. The "noise" can then propagate inside the computational domain and may take a long time to "dissipate" before a stable solution is calculated. 

There are several measures that a user can take to prevent or reduce to a minimum this initial "noise", namely defining a warmup period for different types of forcing. During the warmup period, the forcing function importance is increased slowly (linearly in most cases, some cases exponentially), so that the forcing function is at 100% at the end of the warmup period. This process is also known as ramping. 

Solution

The forcing functions that have a ramping function in OpenFlows FLOOD are tide, wind, atmospheric pressure and baroclinic forces. All the options are available in the Hydrodynamic input option (MOHID Water engine). 

To activate the warmup period for tide, activate Tide to True, and then set the Tide warmup period (in seconds). Typical values range from 6 hours (21600 sec) to 2 days (172000 sec). 

To activate the warmup period for wind, activate Wind to True, and then set the Wind warmup period (in seconds). Typical values range from 6 hours (21600 sec) to 2 days (172000 sec). 

To activate the warmup period for atmospheric pressure, activate Tide to True, and then set the Atmospheric pressure warmup period (in seconds). Typical values range from 6 hours (21600 sec) to 2 days (172000 sec). 

To activate the warmup period for baroclinic forces, activate Baroclinic pressure to True, and then set the Baroclinic pressure warmup period (in seconds). Typical values range from 5 days (432000 sec) to 10 days (864000 sec).