Solution Parameters |
 
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Solution Parameters |
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If convergence problems are experienced in a time domain dynamic analysis, you could try varying the solution parameters. Before resorting to this course of action, you should try to fully understand the model behaviour, and the reasons why the analysis is failing to complete with the existing solution parameters. Possible alterations you might consider might include some of the following:
•Increasing the ramp time.
•Adding, or increasing, damping.
•Relaxing the tolerance measures.
•Utilisation of the Small Torque Value option.
A small level of damping is beneficial in many dynamic analyses in dissipating the effects of transients and high frequency noise. However, what particular values of l (stiffness proportional damping coefficient) and m (mass proportional damping coefficient) represent a small level of damping is very much dependent on the structure under consideration. For this reason, and because it is obviously important to quantify the effect particular values are having on the response in a particular run, it would in general be recommended that you perform a dynamic analysis with no damping, either initially or as a check. Refer to Damping for further information on structural damping.
Note that the default tolerance levels are adequate in the vast majority of cases, and the adjustment options will be rarely invoked. You should be extremely cautious of relaxing the tolerance measures beyond recommended default values, as this could result in cumulative errors in the solution. Refer to Solution Convergence for further information on convergence ratios.
The inclusion of torque in the convergence calculations can in some analyses increase the number of iterations required for convergence. This is particularly true of flexible riser systems subjected to waves and current approaching at an angle oblique to the initial plane of the riser. In reality, the actual torque values may be small, and the influence of torque on the solution (as opposed to the rate of achieving this solution) minimal. The Small Torque Value input can be used in such cases to effectively instruct Flexcom to ignore torque in determining convergence. Refer to Solution Convergence for further information on the small torque value.
•*TOLERANCE is used to define the analysis convergence tolerance measure and related data.
•*DAMPING is used to incorporate damping into a dynamic analysis.