Nastran-Interface manual


Static Loads

This section describes all options that the user can find in the menu Static Loads.

Point Force Load

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This load is applied to one point of a structure. The sign of components is equal to the one defined for the enforced displacements. Figure 1

Moment

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This moment is applied to one point of a structure. A sign of components is equal to the one defined for the enforced displacements (right hand rule). Figure 1

Line-Pressure-Load

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Defines uniformly distributed applied loads to line entities of a geometry (bars, beams and curved beams). It is possible to select the coordinate system for data entries in this load.

Figure 2 – Coordinate System

If the option “BASIC” is selected, all data entries make reference to global (basic) axes. If the option “ELEMENT” is selected, all data entries make reference to local (element) axes. Axes are defined by the user in Local Axes condition (for more information about Local Axes, see Local Axes Condition). Remember that it is necessary to define local axes for every line of structure.

The following figures are examples of differences between “BASIC” and “ELEMENT” coordinate system.

Figure 3 – Pressure Load Y-Element

Figure 4 – Pressure Load Y-Basic

In the Figure 3 (Pressure Load Y-Element), the user selects Element coordinate system. The pressure load is in a direction of Y-Element axis. In the Figure 4 (Pressure Load y-Basic) the user selects Basic coordinate system.

In these two options the total load applies to the beam equals P*L in the Y-Basic direction.

Comment for NASTRAN advanced users:  It is not necessary to mesh to assign this condition. It can be assigned directly over lines of a structure.

Line-Projected-Pressure

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This condition is very similar to the previous one. The coordinate system works the same way, based on the Line-Pressure-Load.

The only difference is that the total load applied to the beam equals P*L*cos (alpha) in the Y-Basic direction, where alphais the angle of the X-Element axis with respect to the X-Basic axis. (See the two previous figures).

Comment for NASTRAN advanced users:  It is not necessary to mesh to assign this condition. It can be assigned directly over lines of a structure.

Line-Triangular-Pressure

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Defines a triangular distributed load to linear elements of a structure. The coordinate system works the same way: Line-Pressure-Load, but in this condition, element axes make reference to element axes and not to the local axes of the line (normally, it is common that element axes are equal to line axes). It is very important to use this condition correctly. Remember that it is only applicable to mesh linear elements.

In this condition it is necessary to introduce a pressure to the start point and a pressure to the end point. To know which ends of the element is the start point, the user has to pay attention to the origin of the X-Element axis.

The following figure is an example of triangular load in Basic coordinate system.

Figure 5 - Triangular Pressure Load

Suggestion: If the user wants to apply this kind of load directly over a line, one option may be mesh with only one liner element all line.

Surface-Pressure-Load

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Defines a pressure load on a surface.

Surface Pressure Load always makes references to global axes.

Normal-Surface-Load

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Defines pressure load acting normal to a surface.

A negative sign of the pressure is inward to the surface.