Hydraulic Gradient Calculation
This option is only available when the fluid is a liquid and there are no properties present in the network. In order to calculate the hydraulic gradient at every node in the network, Pipenet must be supplied with the absolute elevation of one reference node with respect to a datum line.
Giving the reference node label and its height, the hydraulic gradient calculation can be performed. The hydraulic gradient, H, at any point in a fluid is defined as:
Where:
P is the gauge pressure at the point,
Z is the elevation of the point with respect to a datum line,
g is the acceleration due to gravity and
ρ is the fluid density at that point.
In order to calculate the hydraulic gradient at every node in the network, PIPENET must be supplied by the user with the absolute elevation of one reference node with respect to a datum line.
If for any node, H<Z, implying an unfeasible network, a warning message is issued.
Hydraulic gradient calculations may only be performed when the fluid in the network is a liquid.
Ambient Pressure Correction
This option is only available when the fluid is a gas and gauge pressure units are in use. To use the ambient pressure correction facility the user must specify the absolute atmospheric pressure and temperature at a reference node. This is typically used in nuclear installations where the height of a chimney stack can create a draft.
While PIPENET vision performs its calculations using absolute pressure units of Pascals, it allows use of a variety of units for pressure including gauge units such as Bar G and psiG G. Normally the program converts pressures in gauge units to absolute units by adding a constant value of one standard atmosphere (101325 Pa).
In networks with large elevation changes, users may wish to take account of the variation in atmospheric pressure with height when converting from gauge to absolute pressures.
Atmospheric pressure Pi, at a height hi above a datum point is given by the equation.
Where:
P0 is the absolute atmospheric pressure at the datum point,
g is the acceleration due to gravity and
ρ is the fluid density.
To use this correction facility the user must simply supply the absolute atmospheric pressure at a given reference node.
Ambient pressure correction is permitted by PIPENET only when gauge pressure units are being used and the fluid in the network is a gas.
NOTES
1. The use of a default value for Pipe/Duct Roughness is particularly useful when most or all of the pipes/ducts in the network have the same roughness.
2. Some of the lines in this box may be greyed out when not relevant, and cannot be edited. For example it is not possible to set default values for Duct Height or Width when the fluid in the network is a liquid, as ducts cannot be used with liquids, and a default elevation cannot be set if Node Elevation has been selected in the menu option Options | Defaults or Init | Defaults.
Colouration Menu:
This menu contains three items which can be used to setup the colouring of nodes and/or pipes and ducts based on the value of one or more attributes.
Simple rules
This option is used to define the colouring of links and or nodes based on the value of a single attribute or result, for example node elevation, pipe length, velocity of fluid through pipe, and so on.
Complex nodes
This option is used to define more complex colouring rules for nodes based on the values of more than one attribute or result.
Complex links
This option is used to define more complex colouring rules for pipes and ducts based on the values of more than one attribute or result.
Colour Schemes:
Simple Colour Schemes
With simple colour schemes, the user selects a component attribute or result, for example, pipe length, pressure difference, node elevation, and then creates a scheme by associating the selected attribute or result with a set of intervals. The intervals are defined by five values v1, v2, v3, v4, v5, the intervals being:
≤ v1
RED
>v1 & ≤ v2
ORANGE
>v2 & ≤ v3
GREEN
>v3 & ≤ v4
CYAN
>v4 & ≤ v5
BLUE
>v5
MAGENTA
If intervals are not defined they will be provided automatically based on a suitable scaling of the known values for the attributes or results. Note for results the intervals are calculated on the completion of a calculation.
Colour schemes are displayed and edited via the Classes dialog.
This consists of two columns, one for nodes and the other for pipes/nozzles. At the head of each column is a combo box for selecting the colour scheme. Note these two combo boxes have a dual purpose in also selecting which attribute is displayed above a component in the schematic.
Below the combo box are five edit boxes used for defining the six intervals. The coloured boxes alongside the edit boxes define the colours for the six intervals. The edit boxes will be greyed out if the selected colouring scheme does not use intervals.
Immediately below each column of five edit boxes are two check boxes:
Colours On - used to enable/display colours. If this box is unchecked then the default colouring scheme will be used. However, the selected attribute will still be displayed when the Display Attributes buttons are selected.
Auto classify - used to select automatic calculation of ranges following completion of a calculation. If this box is checked then the five values defining the six intervals will be re-calculated each time a calculation is performed.
Use modulus - if this is selected then classification will not take the sign of the attribute into consideration. For example typically the user would be interested in the magnitude of the velocity, rather than whether it is positive or negative.
The final three buttons are used to select the way in which the intervals are coloured, the default being the six colours ordered as RED, ORANGE, GREEN, CYAN, BLUE and MAGENTA. The ordering of the colours may be reversed by selecting the Reverse colours button. As an alternative to the six colours a single colour may be selected to be represented in six shades. Selecting the Graduated button displays a pop-up window via which the colour can be selected.
The two combo boxes for selecting the colour scheme (and hence the attribute to be displayed on the schematic) are reproduced on the Options Toolbar. The Options toolbar can also be used to display legends (one for nodes and one for pipes/ducts) on the schematic. For example:
The legends can be moved around by clicking and dragging with the mouse.
Values are displayed with the correct sign for directional components; negative if the flow is in the opposite direction to the component direction, or positive if it is in the same direction.
Complex rules
Complex rules allow the user to define a colouring rule in a more flexible manner, this is best described by reference to the dialog used to enter a complex colouring rule:
This shows the dialog for entering a complex rule for a pipe or duct, which for a node has the same layout. It comprises:
1. A name for the rule
2. Up to three conditions (only two are used in this example) consisting of an attribute or result name (selectable from a drop down list), a relational operator (again selectable from a drop-down list), a value, and a Use modulus check box (if the box is checked then the absolute value of the attribute must satisfy the condition).
3. Logical ‘And’ or ‘Or’ operators relating the conditions.
4. The colour to be used for display.
http://www.cadfamily.com/html/Article/User%20Interface%20Of%20Pipenet-Part%20B_634_1.htm
http://www.cadfamily.com/html/Article/User%20Interface%20Of%20Pipenet-Part%20B_634_2.htm
http://www.cadfamily.com/html/Article/User%20Interface%20Of%20Pipenet-Part%20B_634_3.htm
http://www.cadfamily.com/html/Article/User%20Interface%20Of%20Pipenet-Part%20B_634_4.htm
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