The sequence concept

To exchange the coupling fields going through OASIS3 main process (i.e. with status EXPORTED, AUXILARY, or EXPOUT, see section 5), in a given order at each coupling timestep, a sequence index SEQ must be defined for each of them. This is not required for I/O fields or for coupling fields exchanged directly between the component models, i.e. with status IGNOUT, INPUT or OUTPUT. SEQ gives the position of the coupling field in the sequence.

Figure 4.6: The SEQ concept

A coupling algorithm, showing the SEQ concept, is illustrated on figure 4.6. All coupling field produced by the source model at the coupling timestep can be ``consumed'' by the target model at the same timestep without causing any deadlock situation; therefore, LAG = 0 for all coupling fields. However, at each coupling timestep, a particular order of exchange must be respected; must be received by model A before it can send , which in turn must be received by model B before it can send . Therefore, SEQ = 1, 2, 3 must be defined respectively for , and . As all fields can be consumed at the time they are produced (LAG=0 for all fields), there no reading/writing from/to coupling restart files.