Stage 2 - Entering The Network

Creating the single pipe

With the schematic and the editable Properties Window, it is a simple task to enter this network.

You simply draw the pipe in the schematic window, and then define the properties of the pipe.

To draw the single pipe, proceed as follows:

1. From the toolbar, select the pipe drawing tool .

2. Place the cursor at the point where you want the input node to appear, and left click.

3. A line representing the link element is drawn, and it tracks mouse movements.

4. Place the cursor at the point where you want the output node to appear, and left click.

5. If, between defining the input node and the output node, you want to abort creation of the link, select the Escape key.

6. Note that, if a pipe is coloured red, this means the pipe is selected, and its properties will appear in the Properties Window.

7. Select the node and pipe label buttons from the display toolbar, if they are not already selected. The network should then appear as show in the schematic representation above.

Now we can add the properties to the pipe; for example, the bore and length of each pipe. Click on the pipe and its current properties appear in the Properties Window.

In this example, the Young's modulus and Poisson's ratio for the pipe material are unavailable, and the default wavespeed is displayed. If some pipe schedules had been defined, they would appear in, and could be selected from, the Pipe Type list. Multiple fittings can be inserted on the pipe if required. An additional factor for the pipe can also be entered in the Additional k-factor field.

Click in the value field for the pipe diameter and enter the value 250, followed by Tab to move to the next field, the length. Enter a value of 1000.0 for the length of the pipe, followed by either Tab or Return to accept the value.

Undefined and invalid components

When a pipe, or in fact any link component, is first drawn in the schematic, it is coloured blue, to indicate that either the component has not had its attributes specified and/or it has an invalid

entered for the component, its colour changes to black (or white, if the background is black).

The colour of a component may revert to blue in either of the following situations:

1. If a check is performed using the check button on the calculation toolbar and the component is found to be invalid.

2. If the file is saved and re-opened, and on re-loading the component it is found to be invalid.

Entering the Specifications

Two specifications are required in this example. The pressure at the downstream end of the pipe is constant, while the pressure at the upstream end varies sinusoidally.

Select the node that is to have the constant specification, and in the Properties window:

1. Select the Specification type as Pressure.

2. Tab to the next field and select the time function as Constant.

3. Tab to the next field and enter the constant value as 0.0.

4. Enter tab or the Return key to complete the editing.

The Properties window should appear as:

Select the other node and, in a similar manner, in the Properties window:

1. Select the specification type as Pressure.

4. Tab and enter the frequency as 0.1.

5. Tab and enter the constant phase as 0.0.

6. Tab and enter the constant value as 50.

7. Tab or select Enter to complete the data entry.

The Properties window should appear as:

Another way to look at pipes is via the Tabular View, although it is not a significant advantage with only one pipe, but makes a lot of sense when there are many pipes whose properties you wish to view. Select the menu option View | Data window to display the window:

Data can be edited in this window simply by clicking in the appropriate cell, and entering a new value or selecting from a list of valid options. Moving to the next field is achieved by either entering a tab or by pressing the Return key.

Both the Schematic Window and the Tabular View can be displayed simultaneously by selecting the menu option Windows | Tile horizontally or Windows | Tile vertically.

Defining the output tables

Simple or Complex tables can be defined. Simple tables contain output results for a single component only. Complex tables can include output results for more than one component. In this example, we shall request output results for pressures and flow rates along the pipe by using two simple tables. Tables are edited via the Tables tab in the Tabular view; selecting the tab displays:

Select the Add button in the heading of the window, and then enter the title as "Pressures along the pipe" in the Title 1 field (the name in the title 1 field appears in the combo box in the window heading), and the window should appear as:

Now select the symbol ... in the first column, adjacent to the column number 1; this expands the information stored, starting in column 1. Now select the component type as Pipe, and the window changes to:

We want to select the inlet pressure, outlet pressure and Pressure at ...(m) option; for the last of these, we must provide a value of 500:

Note that the next available column is now shown as 4.

Creating another table for the flow rate is achieved in a similar manner:

1. Select the Add button to create a new table.

2. Enter the title for the table in the Title 1 field.

3. Select the component type as Pipe again.

4. Select the options inlet flow rate, outlet flow rate and Flow rate at ...(m).

5. Provide the value for the flow rate at 500 m.

The definition should appear thus:

Defining the graphs

Two types of Output Graph are available: (a) variable against time and (b) pipe variable against distance. In this example, we will request graphical output of pipe pressures and flow rates against time.

Graphs can be associated with a component in two ways. In the first way, we right-click on the desired component, choose the option Select Results, with sub-option Variable v Time, and then select All variables:

This is probably the simplest way for our network, since we only have one pipe. The alternative is via the Graphs tab in the Tabular View:

which can also be used for displaying all defined graphs. Firstly, select the ... in the first column of the first available line under the Variable against time section. Next, select the component type as Pipe, the component label as 1, and the variable as All variables (with all of these options being selectable from drop-down lists of available items).

Regardless of the method used, the Result Graphs tabbed window should appear as follows:

The start and stop times for the simulation, together with the output time step for graphical output, are defined in the Calculation | Output dialog (see Stage 4), where a filename for the graphical output can also be defined.