The element-by-element estimate is conservative it will give a smaller stable time increment than the true stability limit that is based upon the maximum frequency of the entire model. This element-by-element estimate is determined using the current dilatational wave speed in each element. In an analysis Abaqus/Explicit initially uses a stability limit based on the highest element frequency in the whole model.
#Hypoelastic connectors abaqus 6.13 code#
Abaqus/Explicit has two strategies for time incrementation control: fully automatic time incrementation (where the code accounts for changes in the stability limit) and fixed time incrementation. In nonlinear problems-those with large deformations and/or nonlinear material response-the highest frequency of the model will continually change, which consequently changes the stability limit. If the mesh contains uniform size elements but contains multiple material descriptions, the element with the highest wave speed will determine the initial time increment. If the model contains only one material type, the initial time increment is directly proportional to the size of the smallest element in the mesh. The total energy balance will also change significantly. When the solution becomes unstable, the time history response of solution variables such as displacements will usually oscillate with increasing amplitudes. Failure to use a small enough time increment will result in an unstable solution. The time increment used in an analysis must be smaller than the stability limit of the central-difference operator. For further discussion, see “Computational cost” below. The time increment chosen by Abaqus/Explicit also accounts for any stiffness behavior in a model associated with penalty contact. In general, the actual stable time increment chosen by Abaqus/Explicit will be less than this estimate by a factor between and 1 in a two-dimensional model and between and 1 in a three-dimensional model. This estimate for is only approximate and in most cases is not a conservative (safe) estimate. When the transverse shear stiffness is defined for shell elements (see “Shell section behavior, ” Section 29.6.4), the stable time increment will also be based on the transverse shear behavior. In general, for beams, conventional shells, and membranes the element thickness or cross-sectional dimensions are not considered in determining the smallest element dimension the stability limit is based upon the midplane or membrane dimensions only. Where is the smallest element dimension in the mesh and is the dilatational wave speed in terms of and, defined below. When degrees of freedom at a node are activated by elements with no mass (e.g., spring, dashpot, or connector elements), care must be taken either to constrain the node or to add mass and inertia as appropriate. When degrees of freedom at a node are activated by elements with a nonzero mass density (e.g., solid, shell, beam) or mass and inertia elements, a nonzero nodal mass or inertia occurs naturally from the assemblage of lumped mass contributions. Nodes that belong to Eulerian elements also do not require mass, since the surrounding Eulerian elements may be void at some time during the simulation. Nodes that are part of a rigid body do not require mass, but the entire rigid body must possess mass and inertia unless constraints are used. More precisely, a nonzero nodal mass must exist unless all activated translational degrees of freedom are constrained and nonzero rotary inertia must exist unless all activated rotational degrees of freedom are constrained. The explicit integration scheme in Abaqus/Explicit requires nodal mass or inertia to exist at all activated degrees of freedom (see “Conventions, ” Section 1.2.2) unless constraints are applied using boundary conditions. Uses a consistent, large-deformation theory-models can undergo large rotations and large deformation Ĭan use a geometrically linear deformation theory-strains and rotations are assumed to be small (see “Defining an analysis, ” Section 6.1.2) Ĭan be used to perform an adiabatic stress analysis if inelastic dissipation is expected to generate heat in the material (see “Adiabatic analysis, ” Section 6.5.4) Ĭan be used to perform quasi-static analyses with complicated contact conditions andĪllows for either automatic or fixed time incrementation to be used-by default, Abaqus/Explicit uses automatic time incrementation with the global time estimator. Is computationally efficient for the analysis of large models with relatively short dynamic response times and for the analysis of extremely discontinuous events or processes Īllows for the definition of very general contact conditions ( “Contact interaction analysis: overview, ” Section 36.1.1)
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