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Frequently Asked Questions (FAQ)
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AnswerThe geometrically nonlinear flattening process takes over the real mesh geometry of the planar, buckling, single curved or double curved surface components from the selected cutting patterns and planarizes these planar components by minimizing the distortion energy assuming a defined material behavior.The iterative calculation used for this is controlled by the parameters in the menu "Calculation Parameters"/"Cutting Patterns" tab.The "Max Number of Iterations" parameter is limiting the scope of the calculation and stops the process when the set maximum iteration is reached. Provided the convergence criterion does not depend on the "Tolerance for Convergence Criterion" parameter in the Convergence range when the maximum iteration has been reached, the program displays error message 10154.If no error message is output by the program, it is reasonable to assume a proper convergence.The error can usually be solved by adjusting the flattening geometry or increasing the maximum number of iterations.
No, that is not possible. The calculation of the foundation parameters in RF-SOILIN is performed iteratively. For the first iteration step, it is necessary that the start values for the foundation parameters are selected internally by the program. With these start values, you can perform a finite element analysis of the FE model in RFEM.
The result is a distribution of the soil pressure. The soil pressure of the first iteration step is included as an initial value in the RF-SOILIN calculation. Together with the stiffness modulus of the entered soil layers, it is possible to calculate the settlement for each finite element. The settlement and soil pressure are then used to calculate the foundation parameters.
In the next iteration step, the new foundation parameters replace the old one and a new finite element analysis is started, which in turn yields a new distribution of overloading pressure. As a convergence criterion, we compare the new distribution of soil pressure with the old one.
As long as the deviation exceeds a certain convergence limit, the new distribution of soil pressure in RF-SOILIN is considered in the calculation of new foundation parameters. When the deviation of the distribution of the soil pressure of two consecutive iteration steps is not reached for the first time, the iteration is ended and the foundation parameters of the last iteration step are output as the result in RF-SOILIN.
In the first iteration step, all members are considered. Before the next step, the program determines which members cannot resist the determined compressive forces due to their definition, for example tension members with negative axial forces. Then, the tension member with the greatest compressive force is removed from the stiffness matrix. Thus, the next iteration step follows.
Next, the member definitions are compared to the determined axial forces. For the next iteration step, the tension member subjected to the highest actions is removed from the stiffness matrix. This procedure is continued until no member is subject to the internal forces that it cannot resist.
In this way, you can often achieve a better convergence behaviour for the system because of redistributing effects. This calculation option requires more time because the program must run through a larger number of iterations. Furthermore, you have to make sure that a sufficient number of possible iterations is set (see the 'Settings' dialog box section in Figure).
For this method, it might also happen that the initially failed member is reinserted, because it is subjected to tension forces due to possible redistribution effects.
The calculation will be done faster. HOWEVER: Since only one iteration has been calculated, the results are only correct if there is also just one iteration required for the calculation. For example, this can be the case of load cases using linear static analysis. Also, object with nonlinear properties, such as tension and compression members, may not fail.
On the contrary, load combinations according to second-order analysis require an iterative calculation. Therefore, the results of one iteration only are not correct.
The number of possible iterations should always be sufficiently high. The number may also be much higher than the actually needed number of iterations, because the program will perform as many iterations as required.
Result Table 4.0 shows the number of performed iterations (see Figure).
Compressive forces in cables or tension members may arise if the number of iterations is not sufficient for this analysis so that the system did not converge. The number of iterations can be specified in the Global Calculation Parameters tab of Calculation Parameters (see figure).
For the maximum number of iterations, the value 100 is preset. However, this does not mean that all iterations will be run. Depending on the structural system, the calculation often converges much earlier.
Check also the settings of Reactivation of Failing Members. If the option 'Assign reduced stiffness to failing members' is selected, small compressive forces may arise.
If this is not justifiable, select the option 'Failing members to be removed individually during successive iterations'. However, you should pay attention to the sufficient maximum number of iterations (see above).
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