How does agents behave in the agent-based model?

Below, you can find statecharts for the different agents we use in our models to simulate operations and maintenance and construction projects. Statecharts are used to describe and model behavior of the agents in the model. First we'll take a look at what a statechart is below.

What is a statechart?

• A statechart (also called a hierarchical state machine) is an extension of a finite state machine (FSM).

• It describes how an agent (or a system) can be in different states, and how it can transition between those states in response to events, conditions, or timeouts.

• Compared to a simple FSM, statecharts add extra expressive power:

  • Hierarchy / nested states (states can contain sub-states)

  • Concurrency or orthogonal regions (independent parts of behavior can run in parallel)

  • Entry / exit actions (you can attach behavior upon entering or leaving states)

  • History / memory (you can remember the last active sub-state when re-entering a composite state)

Asset statecharts

Operational condition

The first statechart illustrates possible operational states an asset can be in:

• Operating: the asset is up and can perform its action (e.g. produce power).
• Stopped: the asset is down due to a failure or hasn't been constructed yet and put into operation.

Fixables (failure modes)

The fixable statechart models the states of a failure mode on the asset. It has different states dependent on the what task is required to bring it back to a stable state.

Logistics statecharts

Personnel transport logistics

The transport statechart shows the behaviour of different logistics that are used to drop technicians off and pick them up at an asset requiring minor work, not a major component replacement for example.

Heavy lift vessel and site crane

This is the statechart with multiple work orders and a defined work order capacity:

1. Logistic chartered: wait until the charter lead time expires.
2. Check if it is time to schedule the logistic.
   1. Is it above the minimum used capacity?
   2. Has the longest waiting time among the assigned work orders expired?
3. Schedule the logistic's mobilizing, preparing transit, transit to the first asset, and jacking up steps.
4. Schedule work on the asset, jacking down, and the next transit steps.
   1. The next transit is either to the next assigned work order, then jacking up; or transit back to port, then demobilizing.
   2. This is repeated until there are no more assigned work orders and the logistic is back at port.
5. The charter period ends and the logistic becomes available for charter when the next failure occurs.

Crane

The crane is used to fix components that are taken to the port. Below, the process diagram showed presents all states a crane goes through when operating.

Work orders

When a work order is created, it means that some maintenance or repair work is required on a WTG. The diagram illustrates how a work order progresses, from its creation to its completion.

There are 3 types of work orders:

• Standard order
• Component replacement order (HLV)
• Component replacement order (towing vessel)

The standard order statechart models the different states when a work order is created for a scheduled or minor corrective maintenance task or a commissioning task.

The major component replacement statechart models how the major component replacement using a site crane or heavy lift vessel requires multiple steps before the actual replacement happens.

The final statechart models the states when a major component replacement requires towing the asset to a port for a repair by a crane in a port.