In this tutorial you will create a Tcl script that:

Tools

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The Tcl commands if, foreach and expr will be used to add logic and mathematical functions to the script.  The command hm_getentityvalue is used to extract information from HyperMesh entities, based on data names.

Data names are generic references to the information that physically define an entity in the HyperMesh environment.  An example of this is the x, y, and z coordinates that define a node location in three-dimensional space.  The available data names for each entity can be found in the HyperMesh Reference Guide Data Names topic.

Data names are accessed using the hm_getentityvalue command.  This command uses the data names available for an entity to return the particular value of interest.  The command will return a value that is either a string or a numeric value, depending on the command syntax and the value stored in that particular data name field.  The basic syntax of the command is:

hm_getentityvalue entity_type id data_name flag

where entity_type is the requested entity type (elements, loads, nodes, etc.), id is the entity ID, the data_name is the data field name of interest, and flag is either 0 or 1 depending on whether the command should return a numeric value (0) or a string (1).

To retrieve the x-component of a force with ID 12, the following command can be used:

set force_x [hm_getentityvalue loads 12 "comp1" 0]

Exercise

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Create a Tcl script to compute the resultant sum of a given selection of forces.  This requires that the script read data from the force entities and manipulate the data to calculate the resultant.  To calculate the resultant of the forces, retrieve the x, y, and z components of the forces and compute a vector sum.

Step 1:  Define the process.

The script should automate the following process:

Step 2:  Determine the data names to use to extract the force components.

The following table lists several relevant data names for force loads:

Steps 3-9:  Create the Tcl script and add logic as necessary.

A Tcl script to perform this function might be similar to the following:

Step 3:  Open a text file and save the file as HM8060.tcl.

Step 4:  Select the desired loads and then add those loads to a list.

The *createmarkpanel command is used to allow the user to graphically select the loads from the HyperMesh interface and add them to the mark.  The command below adds the loads to mark 1.  Once the loads have been added to mark 1, the load ids are assigned to a list called loads_list, using the TCL command set.  Add the following 2 lines to the file HM8060.tcl:

*createmarkpanel loads 1 "Select forces to compute resultant";

set loads_list [hm_getmark loads 1];

Step 5: Initialize the variables for the x, y, and z components.

Use the TCL command set to initialize the variables for the x, y, and z components of force to 0.    These variables will be used later in the script to compute the resultant force for each component.  Add the following 3 lines to the TCL file HM8060.tcl:

set x_comp_sum "0";

set y_comp_sum "0";

set z_comp_sum "0";

Step 6:  Begin an if loop which checks to see if the variable loads_list has values.  If it does, proceed with the macro.

Before calculating the resultant of the forces selected, we should check to make sure that the variable loads_list has values in it.  This is done by using an if loop.  In the if loop below, we are checking that the variable loads_list is not empty.  Add the following line to the TCL file to initialize the if loop:

if {$loads_list != ""} {

Step 7:  Use a foreach loop to iterate through each load in the list loads_list and extract the x, y, and z components using the hm_getentityvalue command and the appropriate data name.

Using a foreach loop, each load in the list loads_list will be iterated through.  Within the foreach loop, each load is referenced by load_id and then the component value is added to the previous loads component’s value.  For example, let’s look at the x component.  Using the set command, the variable x_comp_sum is defined as the previous value of x_comp_sum, plus the x component of the current load.  The x component of the current load is retrieved by using the hm_getentityvalue command and the data name comp1 (all the available data names for loads are shown in the table above).  This process is done for the y and z components as well.  Add the following 4 lines to the TCL file:

   foreach load_id $loads_list {

       set x_comp_sum [expr $x_comp_sum + [hm_getentityvalue

loads $load_id "comp1" 0]];

       set y_comp_sum [expr $y_comp_sum + [hm_getentityvalue

loads $load_id "comp2" 0]];

       set z_comp_sum [expr $z_comp_sum + [hm_getentityvalue

loads $load_id "comp3" 0]];

   }

Step 8: Report the Resultant Force to the user.

Use the command hm_usermessage to report each of the components of the resultant force.  Add the following line to the TCL file:

   hm_usermessage "Resultant force: $x_comp_sum, $y_comp_sum

$z_comp_sum ";

Step 9:  Complete the if loop and report an error message if no loads are found.

To complete the if loop, add an else statement.  Remember the if statement checked to see if the variable loads_list was not empty.  This else statement returns an error message to the user to let them know that no loads were selected.

} else {

   hm_errormessage "No loads selected";

}

Step 10:  Test the script.

source HM8060.tcl

It is often necessary to debug Tcl scripts using the Command Window. This allows you to run the Tcl script and easily review error messages, as well as print out debug information.  Additional details can be found in the Creating Tcl Scripts and Running Tcl Scripts sections.

There are several important assumptions used when creating this script.

If any of these assumptions are not true, the values returned by the script may be invalid.  Additional conditional logic can be programmed to check for each of these situations and an error message can be returned or they can be handled appropriately.

5.   The result of the macro is shown in the status bar.  Either a message with the resultant force is shown or else there is a note saying that no loads were selected.

 

 

See Also:

HyperMesh Tutorials