COMSOL 6.3 - Combo Box

A can function as either a combination of a drop-down list box and an editable text field or as a drop-down list box without editing capabilities.

To illustrate the use of a combo box, consider an application where the user selects one of six different mode shapes to be visualized in a structural vibration analysis. This example uses a Solid Mechanics physics interface with an Eigenfrequency study and is applicable to any such analysis.

This example is a modification of the Tuning Fork app available in the Application Libraries, under COMSOL Multiphysics. The app is first used to determine a prong length corresponding to 440 Hz. It is then saved as an MPH file and edited further by adding forms and form objects.

The six mode shapes correspond to six different eigenfrequencies that the user selects from a combo box:

In this example, the combo box is used to control the value of a string variable mode. The figure below shows the window for this variable.

The figure below shows the window for this combo box.

In the section, you select a scalar variable that should have its value controlled by the combo box and click . In the list of the window of the combo box, choose a method to define a default value for the combo box. The options are (the default) and . For the option, enter a default value in the associated field. The default value entered must be one of the allowed values.

Vibrational modes 1–6 correspond to trivial rigid body modes and are not relevant to this application; the first mode of interest is mode 7. A choice list allows you to hide the actual mode values in the model from the user by only displaying the strings in the column; the first nonrigid body modes are named Fundamental tone, Overtone 1, Overtone 2, and so on.

In the section for , you can add choice lists that contribute allowed values to the combo box. The declaration associated with this example is shown in the figure below.

The string variable mode is allowed to have one of these six values: 7, 8, 9, 10, 11, or 12. The text strings in the column are shown in the combo box.

In the window of the combo box, you can select the checkbox to get a combo box where you can type arbitrary values. These combo boxes can accept any value and are not limited to those defined in the choice lists. In this example, however, only six predefined values are allowed.

For more information on choice lists, see Choice List.

In the section, specify a method to run when the value of the combo box, and thereby the string variable used as the source, is changed by the user. In the present case, the value of the variable mode is changed, and a local method is run, as shown below.

The code for the local method is listed below.

This code links the value of the string mode to the Eigenfrequency setting in the Plot Group pg1. In this case, the string svar takes the values "7", "8", "9", "10", "11", or "12".

The code above can be generated automatically by using the recording facilities of the Method Editor:

The resulting code is shown below.

Now change the string "8" with the variable mode to end up with the code listing above. This will be stored in a method, say, method1. To create the local method associated with the combo box, copy the code from method1. Then, delete method1.

A quicker, but less general way, of using a combo box is to use in combination with . For the example used in this section, you start by enabling and, in the window of the plot group, select the , as shown in the figure below.

In the window, the parameter is visible as . To create a combo box, right-click and select .

The property name is used for a solution parameter. If a solution has two or more parameters, then there are two or more loop levels to choose from.

The figure below shows the window of the corresponding combo box.

The choice list is automatically generated when inserting a combo box using . Note that a choice list generated in this way is not displayed under the node and cannot be modified by the user. For greater flexibility, such as giving names to each parameter or eigenfrequency value, you need to declare the choice list manually, as described in the previous section.

The time parameter list specified in a study step can be used in many places under the node. In an application, the individual time parameters can be accessed in a similar way to what was described in the last section for parameters, by using in combination with .

Axisymmetric Transient Heat Transfer, available in the Application Libraries, under COMSOL Multiphysics. However, the techniques shown here are applicable to any model with a time-dependent solution.

In the window in the figure below, has been used to access the parameter list in a temperature plot.

In , a handle to the list is now available, as shown in the figure below.

By selecting , you can create a combo box using it as , as shown in the figure below.

In this case a built-in choice list is used to defined the valid options for the time parameters.

The combo box can be used for multiple purposes, for example, to update a plot corresponding to a different time parameter. In order for a plot to automatically update when a user uses the combo box to select a new time parameter, add an event to the combo box at the bottom of its window. In the figure below, a method plotT is called for updating a temperature plot.

The line of code below shows the contents of the method plotT:

The end result is a combo box in the application user interface, shown in the figure below, which automatically updates a temperature plot when the user selects a new value for the list.

You can replace the built-in choice list with a custom one, allowing users to select from a specific subset of available parameters. This approach also applies to parametric sweeps.

are available in the Model Builder by right-clicking the node and choosing from the resulting context menu. Configurations provide centralized control over plot groups, ensuring uniform style and dataset values without adjusting each group individually. Each option applies to multiple plot groups in the model tree and allows simultaneous updates.

In addition, the configuration option enables centralized control of default units for a model.

The figure below shows a configuration node added to the Axisymmetric Transient Heat Transfer model. The settings window includes the time list which can be accessed via the functionality, just as in the example in the previous section.

The figure below displays the settings for the plot group, referencing the configuration. In this way, the time used by the plot group is not locally set but instead determined by the configuration setting.

The same reference to the configuration can be made from the other plot groups, for example, the plot group as shown below.

Enabling the functionality makes the time list available from .

The corresponding combo box (with text label) and settings window are shown in the figures below.

The section of the window references a method updatePlots, as shown in the figure below.

The method loops through all plots group tags and updates each plot:

The complete code is listed below:

If only a subset of the plot groups need to be updated, then they can be updated individually by the method, for example:

To automatically update plot groups when using configurations, you can use a method with code similar to the following:

and run this method as a combobox event, when the value of a combobox is changed.

Consider an application where combo boxes are used to select the material. In this case, an activation condition (see Activation Condition) can also be used for greater flexibility in the user interface design.

, available in the Application Libraries, under COMSOL Multiphysics. However, the techniques shown here are applicable to any model with a time-dependent solution.

The figure below shows screenshots from an application where the user can choose between two materials, or , using a combo box named . A second combo box called shows a list of alloys or alloys, according to the choice made in the list.

The material choice is implemented in the embedded model using global materials and a material link, as shown below.

Each material is indexed with a string: mat1, mat2, …, mat5. An event listens for changes to the value of the global variable alloy, where the value is controlled by a combo box. When the value is changed, a method switchAlloy is run, with one line of code listed below.

The figure below shows the declaration of two string variables, material and alloy, which are controlled by the and combo boxes, respectively.

The application utilizes three choice lists: , , and .

An activation condition is used for the and choice lists, as shown in the figure below.

The window for the combo box is shown below.

Note that the combo box uses the material string variable as its source. The choice list is used to define a discrete set of allowed values for the material string variable. The window for the choice list is shown below.

The window for the combo box is shown in the figure below.

Note that the combo box uses both the and the choice lists. The choice list for is shown in the figure below.

The activation condition for the choice list is shown in the figure below.

When creating a combo box, you can use the functionality to reproduce the features of a combo box that exists within the Model Builder. For example, consider an application where a combo box is used to change the element size in a mesh, as in the figure below.

Switch to the Model Builder and select the node (we assume here that the model has just a single mesh). In the window of the node, select (if not already selected). In the settings window for the node, available directly under the node, select the option . Click in the ribbon. This gives access to the combo box for a predefined element size, as shown in the figure below.

Select the green checkbox to the left of the list to make it available as a source for a combo box in the Application Builder. Then, when you return to the Application Builder, you will find that the choice list for mesh size is now revealed as a potential in the for a new combo box.

To insert the combo box object, you have two alternatives:

The corresponding window for the combo box is shown in the figure below.

Changing the to ensures that the element size setting of the model, in this case , is used as the default element size in the application. The choice list, , from the Model Builder is now selected as the choice list for your combo box in the Application Builder. This choice list does not appear as a choice list under the node of the application tree because it is being referenced from the Model Builder. Therefore, if you want a list with a more limited set of choices, you cannot edit it. Instead, you have to remove the predefined list as the of your combo box and create a new choice list of your own by declaring it under the node. For example, you can create a choice list with three entries, as shown in the figure below.

To learn which values are used by the list in the model, use and change the value from to , then to , and then back to . Click and read the values in the autogenerated code. The property name is hauto and the values for , , and are 4, 5, and 6, respectively, as implied by the automatically generated code shown in the lines below.

The hauto property can also take non-integer values. For more information on mesh options, see Data Access for Input Fields.

The figure below shows part of the user interface of the Acoustic Treatment Boundary Calculator app, available in the Application Libraries under the Acoustics Module. The setting is controlled by a combo box with the options , , and .

The figure below shows the corresponding combo box form object in the Form Editor.

The corresponding settings window is shown below.

Here, the string variable backingCondition is defined under the node in the application tree. The value of this string variable determines the physics setting. A combo box allows the app user to modify the value of the string variable, thereby changing the setting. The allowed values of the combo box is determined by the (under ) named , as shown below.

Additionally, the combo box is configured with an event, which runs the method inputChanged whenever the value of the combo box or its associated string variable backingCondition is updated.

When the computation starts (triggered by the user clicking the button in the app), another method, updatePhysics, updates the model’s physics settings based on the value of the backingCondition variable, as shown in the figure below.

The figure below shows the complete user interface of the app.

If the combo box will be used for the purpose of changing units, then a can be used instead of a (you still select it in the section of the window of the combo box).