Abstract
The introduction chapter has provided a main focus on the methodology to minimize the risk of troubleshooting during analysis. A quality mindset and philosophy have been also given as a recommended way of working and as a good practice to follow in order to conduct an analysis properly. In order to minimize the convergence issue that will be described inside this chapter, there are two important phases to keep in mind to perform analysis as milestones of the modeling process: first, the phase (2) shown in Fig. 1.1 and called the specification of work to define precisely what is the main analysis concern, and second, the phase (5) shown in Fig. 1.1, which is related to the inspections of input data gathered to start computing the model. This chapter now will explain some potential causes of troubleshooting in general. Some convergence issues in the model and some tools will be given to avoid or to fix some common problems during the solution processing.
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- 1.
Dashpots are used to model relative velocity-dependent force or torsional resistance. They can also provide viscous energy dissipation mechanisms. Dashpots are often useful in unstable, nonlinear, and static analyses where the modified Riks algorithm is not appropriate and where the automatic time-stepping algorithm is used because sudden shifts in configuration can be controlled by the forces that arise in the dashpots. In such cases the magnitude of the damping must be chosen in conjunction with the time period so that sufficient damping is available to control such difficulties but the damping forces are negligible when a stable static response is obtained.
- 2.
The MPC module provides the basic capability of modeling multi-point constraints. Multi-point constraints are a general way of relating degrees of freedom to one another within a model. They provide an extremely powerful tool which is useful for many modeling problems. An important example is transmitting load between nodes, which are separated in space or are attached to different degrees of freedom such as translations and rotations.
- 3.
It is essentially a spurious deformation mode of a finite-element mesh, resulting from the excitation of zero-energy degrees of freedom. It typically manifests as a patchwork of zigzag or an hourglass, where individual elements are severely deformed, while the overall mesh section is non-deformed. This happens on hexahedral 3D solid reduced integration elements and on the respective tetrahedral 3D shell elements and 2D solid elements.
- 4.
See Abaqus Example Problems Guide v6.14 in Sect. 1.2.1 Snap-through buckling analysis of circular arches.
- 5.
Geometrically nonlinear static problems sometimes involve buckling or collapse behavior, where the load–displacement response shows a negative stiffness and the structure must release strain energy to remain in equilibrium. Alternatively, static equilibrium states during the unstable phase of the response can be found by using the modified Riks method. This method is used for cases where the loading is proportional; that is, where the load magnitudes are governed by a single scalar parameter. The method can provide solutions even in cases of complex, unstable response.
- 6.
Total energy dissipated in the element resulting from automatic static stabilization. Not available for steady-state dynamic analysis.
- 7.
Total energy dissipated per unit volume in the element resulting from static stabilization. Not available for steady-state dynamic analysis.
- 8.
Energy dissipated by automatic stabilization. This includes both volumetric static stabilization and automatic approach of contact pairs (the latter part included only for the whole model).
- 9.
See Abaqus Analysis User’s Guide v6.14 in Sect. 37.1.3 Contact damping.
- 10.
If the explicit solver is used for a static problem, the solution might take a very long time as Abaqus Explicit uses small increments, and then the user may need to carefully choose a loading rate or mass scaling in order to speed it up.
- 11.
“Artificial” strain energy associated with constraints used to remove singular modes (such as hourglass control), and with constraints used to make the drill rotation follow the in-plane rotation of the shell elements.
- 12.
Recoverable strain energy.
Reference
Belytschko T, Ong JSJ, Liu WK, Kennedy JM (1984) Hourglass control in linear and nonlinear problems. Comput Methods Appl Mech Eng 43(3):251–276. http://www.sciencedirect.com/science/article/pii/0045782584900677. ISSN 0045-7825
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Boulbes, R.J. (2020). Analysis Convergence Guidelines . In: Troubleshooting Finite-Element Modeling with Abaqus. Springer, Cham. https://doi.org/10.1007/978-3-030-26740-7_2
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DOI: https://doi.org/10.1007/978-3-030-26740-7_2
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