Code coupling in Kraken

Basics of signalling

When the solver is executed from command line by Cerberus, the solver should read its own input and go through the basic initialization before waiting for further signals from Cerberus.

After each order received from Cerberus, the solver should fulfill the order and wait for further signals from Cerberus.

Basic "function calls"

When the solvers have completed their previous order and are waiting for the next signal from Cerberus, Cerberus will initiate the communication with a single integer indicating which "function call" should be processed.

The function calls that should be supported by the solvers are:

• terminate

• returnPresentTime
• suggestTimeStep
• setTimeStep
• solveTimeStep
• validateTimeStep
• abortTimeStep

• giveInputFieldTemplates
• giveOutputFieldTemplates
• giveFieldData
• takeFieldData

Each of these function calls corresponds to a certain integer, that are listed in some centrally located header (or some such) files for C and Fortran.

The following sections will go through the signalling for each of the function calls

terminate

When Cerberus sends the signal for a solver to terminate. The solver simply exits gracefully. Final results can be collected, processed and printed out. Memory should be freed, and the process should be terminated in the end.

No further signalling takes place after the C->S signal to terminate.

returnPresentTime

The solver should return the time corresponding to the current time point as a double.

After the S->C communication of the value. The solver should wait for further signals from Cerberus.

suggestTimeStep

The solver should return a preferred length for the next time step as a double.

After the S->C communication of the value. The solver should wait for further signals from Cerberus.

setTimeStep

The solver should receive a length for the next time step as a double.

After the C->S communication of the value. The solver should wait for further signals from Cerberus.

solveTimeStep

The solver should execute the solution for the next time step. This can include some initialization and post-processing for the current solution if needed.

After the solution has completed. The solver should wait for further signals from Cerberus.

validateTimeStep

The solver should accept the previous solution as the final solution for the previous time step. The previous time step will not be calculated again.

After any necessary processing has completed. The solver should wait for further signals from Cerberus.

abortTimeStep

The solver should reload the solution from the beginning of the previously solved time step, discarding the end-of-timestep solution. The previous time step will most likely be calculated again. The solver should update its internal time to reflect this change.

After any necessary processing has completed. The solver should wait for further signals from Cerberus.

giveInputFieldTemplates

The solver should communicate, which sorts of fields it is expecting to receive from Cerberus. The communication syntax is as follows:

Direction	Name	Size and type	Content
S->C	NF	1*integer	Number of fields to be provided
The following repeats NF times:
S->C	Lname	1*integer	Length of field name in char excluding terminating character
S->C		Lname*char	Name of the field
S->C		5*integer	Unit of the field in an OpenFOAMish array (see subsection "Field unit array")
S->C		1*integer	Type of the mesh that the field is on (see subsection Mesh types).
S->C		<depends on mesh>	Mesh data, see sub section Mesh types

After the solver has finished sending data to Cerberus, it should wait for further signals from Cerberus.

giveOutputFieldTemplates

The solver should communicate, which sorts of fields it is expecting to provide to Cerberus. The communication syntax is as follows:

Direction	Name	Size and type	Content
S->C	NF	1*integer	Number of fields to be provided
The following repeats NF times:
S->C	Lname	1*integer	Length of field name in char excluding terminating character
S->C		Lname*char	Name of the field
S->C		5*integer	Unit of the field in an OpenFOAMish array (see subsection "Field unit array")
S->C		1*integer	Type of the mesh that the field is on (see subsection Mesh types).
S->C		<depends on mesh>	Mesh data, see sub section Mesh types

After the solver has finished sending data to Cerberus, it should wait for further signals from Cerberus.

giveFieldData

The solver should provide the data for the field requested by Cerberus.

The communication syntax is as follows:

Direction	Name	Size and type	Content
C->S	Lname	1*integer	Length of field name to be passed (in char excluding terminating character).
C->S		Lname*char	Name of the field to be passed
S->C	NV	1*integer	Number of values to be passed.
S->C		NV*double	The values for the field.

After the solver has finished passing data to Cerberus, it should wait for further signals from Cerberus.

Field unit array

The field unit array consists of 5 integers (e.g. 1 –3 0 0 0 for mass density) specifying the dimension for each of the 5 SI base units for the field

No.	Property	Unit
1	Mass	kilogram (kg)
2	Length	metre (m)
3	Time	second (s)
4	Temperature	Kelvin (K)
5	Quantity	mole (mol)

This means that some of the basic fields that we might transfer will have types of

Field name	SI unit	Basic unit	Unit array
Mass density	kg/m3	kg*m-3	1 –3 0 0 0
Temperature	K	K	0 0 0 1 0
Power (integral)	W	kg*m2*s-3	1 2 –3 0 0
Power density	W/m3	kg*m-1*s-3	1 –1 –3 0 0