About Prescribed Conditions

Complex time- or frequency-dependent boundary conditions, loads, and predefined fields can be specified by referring to an amplitude curve in the prescribed condition definition. Amplitude curves are explained in Amplitude Curves.

In Abaqus/Standard if no amplitude is referenced from the boundary condition, loading, or predefined field definition, the total magnitude can be applied instantaneously at the start of the step and remain constant throughout the step (a “step” variation) or it can vary linearly over the step from the value at the end of the previous step (or from zero at the start of the analysis) to the magnitude given (a “ramp” variation). You choose the type of variation when you define the step; the default variation depends on the procedure chosen, as shown in Defining an Analysis.

In Abaqus/Standard the variation of many prescribed conditions can be defined in user subroutines. In this case the magnitude of the variable can vary in any way with position and time. The magnitude variation for prescribing and removing conditions must be specified in the subroutine (see User Subroutines and Utilities).

In Abaqus/Explicit if no amplitude is referenced from the boundary condition or loading definition, the total value will be applied instantaneously at the start of the step and will remain constant throughout the step (a “step” variation), although Abaqus/Explicit does not admit jumps in displacement (see Boundary Conditions). If no amplitude is referenced from a predefined field definition, the total magnitude will vary linearly over the step from the value at the end of the previous step (or from zero at the start of the analysis) to the magnitude given (a “ramp” variation).

When boundary conditions are removed (see Boundary Conditions), the boundary condition (displacement or rotation constraint in stress/displacement analysis) is converted to an applied conjugate flux (force or moment in stress/displacement analysis) at the beginning of the step. This flux magnitude is set to zero with a “step” or “ramp” variation depending on the procedure chosen, as discussed in Defining an Analysis. Similarly, when loads and predefined fields are removed, the load is set to zero and the predefined field is set to its initial value.

You can define a local coordinate system at a node as described in Transformed Coordinate Systems. Then, all input data for concentrated force and moment loading and for displacement and rotation boundary conditions are given in the local system.

Table 1. Available loads and predefined fields.

Loads and predefined fields	Procedures
Added mass (concentrated and distributed)	Abaqus/Aqua eigenfrequency extraction analysis (Natural Frequency Extraction)
Base motion	Procedures based on eigenmodes:
	Transient Modal Dynamic Analysis
	Mode-Based Steady-State Dynamic Analysis
	Response Spectrum Analysis
	Random Response Analysis
Boundary condition with a nonzero prescribed boundary	All procedures except those based on eigenmodes
Connector motionConnector load	All relevant procedures except modal extraction, buckling, those based on eigenmodes, and direct steady-state dynamics
Cross-correlation property	Random Response Analysis
Current density (concentrated and distributed)	Coupled Thermal-Electrical Analysis
	Fully Coupled Thermal-Electrical-Structural Analysis
Current density vector	Eddy Current Analysis
Electric charge (concentrated and distributed)	Piezoelectric Analysis
Equivalent pressure stress	Mass Diffusion Analysis
Film coefficient and associated sink temperature	All procedures involving temperature degrees of freedom
Fluid flux	Analysis involving hydrostatic fluid elements
Fluid mass flow rate	Analysis involving convective heat transfer elements
Flux (concentrated and distributed)	All procedures involving temperature degrees of freedomMass Diffusion Analysis
Force and moment (concentrated and distributed)	All procedures with displacement degrees of freedom except response spectrum
Incident wave loading	Direct-integration dynamic analysis (Implicit Dynamic Analysis Using Direct Integration) involving solid and/or fluid elements undergoing shock loading
Pore fluid pressure as a predefined field	Static Stress Analysis
	Explicit Dynamic Analysis
Predefined field variable	All procedures except those based on eigenmodes
Seepage coefficient and associated sink pore pressureDistributed seepage flow	Coupled Pore Fluid Diffusion and Stress Analysis
Substructure load	All procedures involving the use of substructures
Temperature as a predefined field	All procedures except adiabatic analysis, mode-based procedures, and procedures involving temperature degrees of freedom

With the exception of concentrated added mass and distributed added mass, no loads can be applied in eigenfrequency extraction analysis.