6. Convergence settings

The keyword factor CONVERGENCE allows you to control the convergence parameters of the calculation.

The ITER_GLOB_MAXI keyword gives the maximum number of iterations performed to solve the global problem at every moment. The excessive increase in this parameter is generally a sign of a problem in modeling or a temporal discretization inadequate.

There are two convergence criteria: RESI_GLOB_RELA in relative and RESI_GLOB_MAXI in absolute. If you don’t fill in anything, then everything happens as if RESI_GLOB_RELA = 1.E-6.

For RESI_GLOB_MAXI =resmax, the algorithm continues global iterations as long as

\[\]

underset {i=1,dots,mathrm {nbddl}} {max} {F} ^ {n}

> text {resmax}

where \({F}^{n}\) is the residue of iteration n (Cf. [R5.03.01] for more details). If this operand is absent, the test is not performed.

For RESI_GLOB_RELA =resrel, the algorithm continues global iterations as long as:

\[\]

underset {i=1,dots,mathrm {nbddl}} {max} {F} ^ {n}

> text {resrel}. {max} L

where \(L\) is the vector of the imposed load and the support reactions (Cf. [R5.03.01] for more details).

When loading and support reactions become zero, that is, when \(L\) is null (for example in the case of a total discharge), RESI_GLOB_RELA is displayed at -1, and we try to move from relative convergence criterion RESI_GLOB_RELA to convergence criterion absolute RESI_GLOB_MAXI. This operation is transparent to the user (alarm message sent in the.mess file). When the vector \(L\) becomes different from zero again, we automatically go back to the criterion of relative convergence RESI_GLOB_RELA.

However, this failover mechanism cannot work at the first step of time. Indeed, to find a reasonable value of RESI_GLOB_MAXI automatically (since the user did not enter it), we need to have had at least one step converged on a RESI_GLOB_RELA mode. Therefore, if the load is zero from the first moment, the calculation stops. The user should already then check that the null load is normal. from the point of view of the modeling he carries out, and if this is the case, find another convergence criterion (RESI_GLOB_MAXI for example).

If both RESI_GLOB_RELA and RESI_GLOB_MAXI are present, both tests are performed.