Multiple Load Case Analysis

A load case refers to a set of loads, temperatures, boundary conditions, and base motions comprising a particular loading condition. For example, in a simplified model the operational environment of an airplane might be broken into five load cases: (1) take-off, (2) climb, (3) cruise, (4) descent, and (5) landing. Often a load case is defined in terms of unit loads or prescribed boundary conditions, and a multiple load case analysis refers to the simultaneous solution for the responses of each load case in a set of such load cases. These responses can then be scaled and linearly combined during postprocessing to represent the actual loading environment. Other postprocessing manipulations on load cases are also common, such as finding the maximum von Mises stress among all load cases. These types of load case manipulations can be requested in the Visualization module of Abaqus/CAE (see the Introduction).

A multiple load case analysis is conceptually equivalent to a multiple step analysis in which the load case definitions are mapped to consecutive perturbation steps. However, a multiple load case analysis is generally much more efficient than the equivalent multiple step analysis. The exception occurs when a large number of boundary conditions exist that are not common to all load cases (that is, degrees of freedom are constrained in one load case but not others). It is difficult to define what “large” is since it is model dependent. The relative performance of the two analysis methods can be assessed by performing a data check analysis for both the multiple load case analysis and the equivalent multiple step analysis. The data check analysis writes resource information for each step to the data file, including the maximum wavefront, number of floating point operations, and minimum memory required. If these numbers are noticeably larger for the multiple load case step compared to those across all steps of the equivalent multiple step analysis (the number of floating point operations can be summed over all steps before comparing), the multiple step analysis is more efficient.

Although generally more efficient, the multiple load case analysis may consume more memory and disk space than an equivalent multiple step analysis. Thus, for large problems or problems with many load cases it is again advisable, as described above, to compare resource usage between the multiple load case analysis and the equivalent multiple step analysis. If resource requirements for the multiple load case analysis are deemed too large, consider dividing the load cases among a few steps. The resulting analysis (a hybrid of multiple load cases and multiple steps) requires fewer resources while retaining an efficiency advantage over an equivalent pure multiple step analysis.

You define a load case within a static perturbation, direct-solution steady-state dynamic, and SIM-based steady-state dynamic analyses. Load case definitions do not propagate to subsequent steps. Only the following types of prescribed conditions can be specified within a load case definition:

• Boundary conditions

• Concentrated loads

• Distributed loads

• Distributed surface loads

• Predefined temperature fields

• Inertia-based loads

• Base motions

• Output requests to the output database

Additional rules governing these prescribed conditions are described in the sections that follow. No other types of prescribed conditions can appear in a step that contains load case definitions. All other valid analysis components, such as output requests to the data file, must be specified outside load case definitions.

Each load case definition is assigned a name for postprocessing purposes.

LOAD CASE, NAME=name
END LOAD CASE

LOAD CASE, NAME=name, GENERATE
END LOAD CASE

Load module: Create Load Case: Name: name