WTIV performs two tasks at the same time during phase overlap

[nRiccobo]

While reviewing the phase overlap feature in ORBIT, we discovered a bug that creates an unrealistic situation. This specifically impacts a fixed bottom project that is hoping to utilize phase overlapping to begin installing turbines before all the monopiles have been installed. The issue lies in the MonopileInstallation and TurbineInstallation class, where each specifically require the wtiv to install the monopiles and turbines, respectively. Note that this isn't an issue with no overlap, because the WTIV simply begins installing turbines once it completes all the monopiles.

However, if the user wants to start installing turbines when the monopile installation phase is 80% complete, then the WTIV ends up performing multiple tasks at once (wrap up the monopiles and starts the turbines). See the figure below, where one of the last tasks for monopile installation is Bolt TP (~364-368hrs) and it occupies the same time span as one of the first turbine installation steps, Attach Tower Section (~365-371hrs). This effectively means that the WTIV is simultaneously doing monopile and turbine installation steps. Because the one vessel can't be in two places at once and these steps happen in parallel, the total project time is not simulated properly.

Note that this only occurs when for fixed bottom projects that select overlapping phases between the MonopileInstallation and TurbineInstallation phases. Additionally, the issue gets worse if the overlap is large (i.e. 20% monopile completion). A fix is to update the MonopileInstallation to not default using the WTIV because realistically, there would be a dedicated vessel that specializes in monopile pile-driving, and the WTIV only installs the turbine.

[sbredenk]

I would add that currently the turbine and monopile phases both use "wtiv"s for installation, which creates a single agent for both installations. In reality, there are usually different classes of vessels used for each phase so there should be an option for additional expected vessel named monopile_installation_vessel or similar that creates its own agent.