Time domain is an essential component of the IDAES framework. When a user first declares a Flowsheet model a time domain is created, the form of which depends on whether the Flowsheet is declared to be dynamic or steady-state (see FlowsheetBlock). In situations where the user makes use of nested flowsheets, each sub-flowsheet refers to its parent flowsheet for the time domain.
Different models may handle the time domain differently, but in general all IDAES models refer to the time domain of their parent flowsheet. The only exception to this are blocks associated with Property calculations. PropertyBlocks represent the state of the material at a single point in space and time, and thus do not contain the time domain. Instead, PropertyBlocks are indexed by time (and space where applicable) - i.e. there is a separate PropertyBlock for each point in time. The user should keep this in mind when working with IDAES models, as it is important for understanding where the time index appears within a model.
In order to facilitate referencing of the time domain, all Flowsheet objects have a time configuration argument which is a reference to the time domain for that flowsheet. All IDAES models contain a flowsheet method which returns the parent flowsheet object, thus a reference to the time domain can always be found using the following code: flowsheet().config.time.
Another important thing to note is that steady-state models do contain a time domain. While the time domain for steady-stage models is a single point at time = 0.0, they still contain a reference to the time domain and the components (e.g. PropertyBlocks) are indexed by time.