id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc
5256	Non-linear system iterations	contacto@…	Francesco Casella	"Good afternoon,

I'm modeling thermo-fluid systems with OpenModelica.

These vectorial equations ""produce"" an algebraic loop (see model ""AlgebraicLoop.test""):

  Dn = VaporDn(P = P, T = T);
  Hn = VaporHn(P = P, T = T);

The thermo functions are highly dependent on temperature.

Every time that the algebraic loop is solved, a lot of iterations are needed:

############ Solve nonlinear system 37 at time 1 ############
initial variable values:
[ 1]                       volume.P  =        100169.17         nom =           100000
[ 2]                       volume.T  =        499.97788         nom =              300
Solution status: SOLVED
 number of iterations           : 1263
 number of function evaluations : 4588
 number of jacobian evaluations : 1263
solution values:
[ 1]                       volume.P  =        100169.17
[ 2]                       volume.T  =        499.97788

Even when the initial values are really close to the solution, a lot of iterations are needed. Why is this happening?

My time step is 1 second and the solver dassl.

The thermo belongs to my company, is there a way to share the package only with the developers?

Thanks in advance

Jose
"	defect	assigned	high		Run-time	v1.13.0-dev.beta1		non-linear solver, external function