Simple example

Functions and protocols used by these two submodels have been grouped in a C-library. With this, it is simple to develop third-party applications – for example: setting up a co-simulation between Simcenter Amesim and a CFD or FEM program.

The following code presents a socket application. This code will act as a client. It will receive one value from the server and send back a constant value equal to 2.0.

The following code needs to be linked against generic_cosim library. This example is provided in Simcenter Amesim demo called TCP_C_Server.ame. You may find the following code and its attached makefile.

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/** This source file demonstrates the usage of libcosim to exchange values 
 * between Simcenter Amesim and an extern C executable with TCP/IP */
 
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>

#include "amecommunication_socket.h"

#define MAX_LINE_LENGTH 4096

int main(int argc, char **argv)
{
  int ret;
  int numberOfInputs=1, numberOfOutputs=1;
  double *input, *output;
  double local_time, next_meeting_time=-1., time_step=.001;
  amesock_conn_attributes socket_id;

  if(argc != 3)
  {
   printf("usage: Appli_socketExample server_name port\n");
   return -1;
  }

  printf("Attempt to connect to %s:%d with 1 inputs, 1 outputs\n", argv[1], atoi(argv[2]));

  /* the number of input/output takes into account 2 extra values : 
  * the next meeting point and local time.
  * that's why nb_input and nb_output are not equal to 1 but 3. */

  /* Simcenter Amesim network submodels behaves this way:
  * Exchanges are synchronized. Master sets up date called meeting point,
  * and then both exectuables are supposed to call amesock_exchange at these dates. 
  * if Simcenter Amesim model is configured as master: it set up next meeting point and
  * expects the compagnion executable to call amesock_exchange on next meeting
  * point so that datas can be exchanged at this date.
  * if slave: it receives next meeting point from compagnion and will call
  * amesock_exchange when Simcenter Amesim time reaches next meeting point. Obviously,
  * master must also called amesock_exchange when it reaches next meeting
  * point */
  
  if(amesock_init(&socket_id,  /* socket identifier */
          0,       /* this socket is not server : it will receives
                  meeting points from server */
          argv[1],    /* server name */
          atoi(argv[2]), /* server port */
          3,       /* number of data to send through the socket (nb_input+2)*/
          3       /* number of data receives from socket (nb_output+2) */
          )!=SUCCESS)
  {
   printf("failed to initialize socket\n");
   return -1;
  }

  printf("Connection initialized.\n");

  input = (double *)calloc(2+numberOfInputs, sizeof(double));
  output = (double *)calloc(2+numberOfOutputs, sizeof(double));
  input[0] = 0; /* input[0] is for next_meeting point.
          It has no influence since we are not master */
  printf("next meeting\tdistant time\tvalue\n");
  for(local_time = 0; local_time < 10; local_time += time_step)
  {
   if(local_time > next_meeting_time)
   {
     input[1] = local_time;      /* input[1] contains the local time */
     input[2] = sin(6.28*local_time); /* value to exchange */
     if((ret = amesock_exchange(&socket_id, input, output))==SUCCESS)
     {
      /* ouput contains :
        output[0]: next meeting point,
        output[1]: distant time,
        output[2]: exchanged value */
      next_meeting_time = output[0];  /* next meeting point from master */
      printf("%lf\t%lf\t%lf\n", output[0], output[1], output[2]);
     }
     else
     {
      if(ret == CONNECTION_SHUTDOWN)
        printf("simulation terminated\n");
      else
        printf("an error occurs while data exchange\n");
      break;
     }
   }
  }

  /* close connection */
  amesock_close(&socket_id);

  free(input);
  free(output);
  return 0;
}