[Linear Perturbation Analysis / ABAQUS]

[Brian Lee]

A linear perturbation analysis is subject to the following restrictions:

Since a linear perturbation analysis has no time period, amplitude references (``Amplitude curves,'' Section 19.1.2) can be used only to specify loads or boundary conditions as functions of frequency (in a steady-state dynamics analysis) or to define base motion (in mode-based dynamics procedures).

A general dynamic analysis (``Dynamic analysis using direct integration,'' Section 6.3.2) cannot be interrupted to perform perturbation analyses: before performing the perturbation analysis, ABAQUS requires that the structure be brought into static equilibrium.

During a linear perturbation analysis step, the model's response is defined by its linear elastic (or viscoelastic) stiffness at the base state. Plasticity and other inelastic effects are ignored. For hyperelasticity (``Hyperelastic behavior,'' Section 10.5.1) or hypoelasticity (``Hypoelastic behavior,'' Section 10.4.1), the tangent elastic moduli in the base state are used. If cracking has occurred--for example, in the concrete model (``Concrete smeared cracking,'' Section 11.5.1)--the damaged elastic (secant) moduli are used.

Contact conditions cannot change during a linear perturbation analysis; they remain as they were defined in the base state. Frictional slipping is not allowed during linear perturbation analyses; all points in contact are assumed to be sticking if friction is present.

The effects of temperature and field variable perturbations are ignored for materials that are dependent on temperature and field variables. However, temperature perturbations will produce perturbations of thermal strain.

If geometric nonlinearity(NLGEOM) is included in the general analysis upon which a linear perturbation study is based, stress stiffening or softening effects and load stiffness effects (from pressure and other follower forces) are included in the linear perturbation analysis

[Brian Lee]

nlgeom을 linear perturbation step에 쓰더라도 geometric nonlinearity effect는 적용되지 않으며, 여기서 이야기하는 것은 linear perturbation step 이후의 general step에 대해 적용이 유효하다는 것이다.