This is the first in a series of posts looking at how we can use Mermaid to:
- Analyse a large offshore operation;
- Make decisions about which vessels and strategies we want to use;
- Optimise our offshore operation.
We’re going to perform a series of simulations to help determine what vessel and strategy we should use and when we should perform the work. This is a fictitious case so we’ll throw a few constraints and assumptions in as we go just to make it interesting.
We are analysing the installation of monopile foundations and transition pieces for an offshore windfarm in the North Sea. We’re starting with an analysis which is part of our suite of training materials and may look familiar to any readers who’ve completed “Introduction to Mermaid”.
An overview of the flow diagram is shown in the image above. The operation is comprised of two main parts, the Loading Cycle and the Installation Cycle. The first of these represents the in-port operations for loading the required components and tools onto the installation vessel and the second the at site operations required to perform the foundation installation.
The loading is modelled as being performed using the instalaltion vessel’s own crane and and it is assumed that the components and tools are stored on a barge which remains in the home port. A number of operations are defined and their durations and operating limits, including suspendability, defined.
The installation is shown above. Firstly, note that no transits are specified. Mermaid uses task locations to automatically schedule the movement of vessels (I’ll talk about this a little more later later).
The installation is modelled as a number of sub-groups within one larger fully suspendable group. This means that appropriate breaks in work can occur if poor weather occurs. As with the loading durations and limits are specified on all the tasks to be performed.
The entire installation process (the large dark blue group in the first image) is repeated multiple times until each foundation in the wind farm has been installed.
The large heavy lift vessel used is shown below. I’ve included some indicative costs and metocean and transit limits, the port access limits are not shown, but the vessel has unlimited access to its home port.
I noted before that transits are not explicitly specified in the flow diagram, instead the changing location of work and the requirements to shelter from storms (when the on station limits are exceeded) trigger movement. Mermaid analyses these transits so that the appropriate access and depart limits are used and conformed to, and the vessel transit speed limits are applied.
Finally, we’ve decided that this vessel can carry sufficient supplies to perform one foundation installation per trip out of port, so there’s going to be a lot of transiting back and forth.
Since we want to try to work out, among other things, when we should be looking to do this work, we’re going to run the analysis starting every two weeks across our entire metocean data set. This will give us a vast quantity of data to analyse and inform both our later simulations and our decision making.
Now we’ve defined a vessel which we may want to use, and a series of operational steps we can take to install these foundations, we’re ready to give the analysis a run. We’ll do two runs to start with; the first installing just 10 foundations and the second installing all 72 foundations. The first and shorter installation gives us a sanity check on our set up before performing the longer analysis.
The Next Steps
Here we’ve introduced our base case and discussed the runs we’re going to perform at this first stage of our analysis/decision making process. In the next post we’ll take a look at the results we generated and have a think about their meaning and our next steps.