I would like to write a user subroutine that modifies the boundary conditions of a job at each increment, based on values it receives from a TCP/IP socket connection. The first problem/question is:
Can I write custom user subroutines for Abaqus other than the default ones or can I modify the UEXTERNALDB to call a "TCP/IP socket server module" to wait for data at a port, then use the data to modify the boundary conditions and then output the resulting displacement data as the response to the external client. The reason for this complexity is to allow me get this data as soon as it is ready instead of waiting for the files to be written to disk and accessing the obd.
You can use UEXTERNALDB to wait for external data (as long as you run on a single processor, otherwise, I'm not sure).
If you want to change things inside your model, you then have to communicate the input to other subroutines (like user-defined boundary condition), usually via a COMMON block.
Thank you Martin. There is very little information on UEXTERNALDB and I believe the UEXTERNALDB waits for the data in a file as well as writes to file the data required. I am trying to prevent disk write operations which is time consuming, hence the need for TCP/IP libraries.
So I will answer this question now that I have solved the issue for anyone else requiring it.
The DISP subroutine allows the user to modify the boundary conditions at the given nodes. The nodes have to be set to be user-defined in the model or if working with the input file (which I hate) then the boundary is specified as:
*Boundary, user
This has to be done to use the DISP. It's a shame there is very poor documentation on ABAQUS subroutines and turorials for using them.
Next the UEXTERNALDB allows you access to the LOP variable which informs on when the subroutines are called. It should be used to know when to open references, files, connections. Typically LOP=0 is the start of an analysis or LOP=5 is the start of a restart analysis and these should be used to open the references/files/connections. LOP=6 should be used to close these references.
Next the external communication - UEXTERNALDB gives the ability to write to file and read from the file by default but that functionality can be extended using an external winsock library which I found very useful (this library is ws2_32 which is part of the Visual Studio package so no need to add new modules. The initialisation, send, receive, closeconnection functions can be written in the same subroutine file as the DISP and UEXTERNALDB).
The winsock library allows me to open a connection to a server (at LOP=0) then feed current state of the system in real time at increment start to the server that replies with target boundary conditions that then feed to the DISP subroutine using common global variables.
This has been tested so far and it is fully functional and working. *Have not got around to extracting current reaction forces yet with GETVRM or something similar but it should be easier to accomplish now. Hopefully, this gets someone through difficulties experienced.*
UPDATE: Last statement was not possible. Had to add node print commands in the input file by editing model keywords in ABAQUS CAE. Then use URDFIL to extract the reaction forces written to a txt file by the node print system.
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