Following are several basic concepts and definitions that provide important information about the Loads and Boundary Conditions application.

In Patran, loads and boundary conditions are treated as a single type of data to be assigned to portions of your geometry or finite element model. As mentioned above, the specific load and boundary condition data which you can assign is highly analysis-dependent. The analysis preference which you set upon entry to your database, or define later via the Preferences/Analysis menu option, determines which options are available to you when you use the Loads/BCs application form in Patran.

As a result, the kinds of load and boundary condition data which you can specify may vary from the examples shown in this guide, which use preferences available for MSC Nastran. Nonetheless, there are several basic kinds of loads and boundary conditions which are common to many of the most popular finite element analysis programs available today. The following subsections describe some of the more general types you may encounter.

Beyond the three basic kinds of analyses described below, there are many additional analysis types, including acoustic, electromagnetic, and frequency response, to name a few. Each of these kinds of analysis has its own unique loads and boundary conditions, based upon the capabilities of the analysis software you are using in tandem with Patran. The actual loads and boundary conditions that you will use depend a great deal upon the behavior you are trying to simulate and the engineering assumptions that you make in your model.

In a structural analysis problem, you are generally trying to determine the response of a model to physical loading, or specific structural behavior such as frequency response or buckling. Some of the loads and boundary conditions you may work with include force, pressure, velocity, inertial loads, displacement, temperature, and contact.

Thermal analysis problems, which determine the response of a model and its materials to thermal conditions, include loads and boundary conditions such as heat sources, heat flux, convection, radiation emissivity, and view factor. Note that the temperature values that often form the output of a thermal analysis may subsequently be used themselves as loads in other types of analyses, such as structural problems. The use of output quantities as loads is supported in Patran using a field capability known as FEM fields, discussed later in this chapter.

Fluid dynamics analyses simulate the behavior of fluid flow, and feature inputs such as velocity fields, pressures, and temperature.

Load cases contain loads and boundary conditions used within a single analysis solution. For example, one load case may represent the loads and BC for each time point in a time-dependent analysis, or a single state of loading for one of many static problems. They are central to the ability to perform complex analyses on an individual model, or examine multiple states of loading and behavior within the
same model.

There is a default load case that, in the absence of specifying your own load cases, contains any loads or boundary conditions defined for your model. For basic single-state problems, such as static structural or steady state thermal analysis, this default load case is often sufficient. For more complex analyses, or for multiple cases of simpler behavior within an analysis, specific load cases must be defined.

One of the most elegant features in Patran is its ability to create fields that describes the variation of the values of an analysis quantity, including loads and boundary condition objects, material properties, and element properties.

Once you have defined a set of fields, you can easily select them as values on the Input Data subform for the Loads and Boundary Conditions application, instead of entering a constant. Moreover, Patran presents a list of the fields that are available whenever you click in an appropriate databox. Following are descriptions of the four main types of fields: