Subsections

• Internal Load Curves
• External Load Curves

Load Curves defined by FEMGEN Load Types

Load curves are also defined in FEMGEN via the following load types:

TR-CURVE 		 For transient dynamic analysis only
DY-CURVE 		 For dynamic relaxation analysis only
DT-CURVE 		 For both transient dynamic and dynamic relaxation analysis 
FL-CURVE 		 For all of the above but drawn from a file 

Load curves can be associated with the FEMGEN load types detailed in Chapter 9 (DISP, R-DISP, VEL, R-VEL, ACCEL, R-ACCEL, PRESSURE, FORCE, and TEMPERAT). The association between a load curve and an actual load is achieved via the load case number. A given load will thus be associated with the load curve which has the same loadcase number. More than one load can have the same loadcase number and thus reference the same load curve. There can only be one load curve per loadcase.

The interface will issue a warning if there is more than one load curve for a single loadcase and will ignore all curves after the first one defined for a given loadcase. The interface will create a flat, unit load curve (termination time 1.0 seconds) where a load has been defined and there is no corresponding load curve definition. The interface issues a warning when this happens.

The points which define a load curve can either be entered at the FEMGEN command line (internal load curves), or drawn from a file of point pairs (external load curves). There is a limit of 45 points (time, value) for internal load curves and no limit for external load curves.

Internal Load Curves

Transient dynamic only, dynamic relaxation only, and transiant dynamic/dynamic relaxation load curves are supported via load types TR-CURVE, DY-CURVE, and DT-CURVE. All curves have the same parameters which are up to 45 pairs of values given as (time, value). The interface will truncate the list which the user gives at the last zero value after time zero. For load curves with negative values it is thus important not to place a time point exactly on the zero datum. The FEMGEN command to define a dynamic curve is as follows (transient and dynamic/transient differ only in load type name):

PROPERTY LOADS DY-CURVE [load_name] loadcase part t₁ v₁ ... t_n v_n

The load name can be anything. The part name is needed because all FEMGEN loads must be attached to one but the actual part information is not used by the command. Attaching the load to a point will ensure that the default FEMGEN load display is not spoilt by load curve data.

External Load Curves

An external load curve definition is also supported. This allows load curve data cards (in free format as time, value) to be drawn directly from a named file in a directory specified by environment variable FG_PRE_CRV (see section 1.4).

This type of load curve data is accessed via the FL-CURVE load type with the name of the file supplied as the load curve name for example:

PROPERTY LOADS FL-CURVE file_name loadcase part curve_type

The curve_type parameter can be set to 0, 1, or 2 depending upon whether the curve is to apply to transient dynamic analysis, dynamic relaxation analysis, or both. The part name is needed because all FEMGEN loads must be attached to one but the actual part information is not used by the command. Attaching the load to a point will ensure that the default FEMGEN load display is not spoilt by load curve data.

A load curve file for an analysis lasting 0.1 seconds could look like this:

   0    0
   0.05 1
   0.1   1.0