In addition to adding mass to a Pipe via an initial/boundary condition, and adding/removing mass via mass flux links, GoldSim allows you to instantaneously add species mass to a Pipe.
This is done using the Discrete Changes field in the Pipe dialog, which is located toward the bottom of the “Basic Pipe Properties” section:
This field only accepts discrete change signals. The discrete change signal must be a vector by species and have dimensions of mass. Typically, such a discrete change signal will be the output of a Discrete Change element that has been triggered by an event.
Discrete change signals have an instruction associated with them. Two types of instructions are possible: Add and Replace. The Discrete Changes field for a Pipe only accepts Add signals.
When an Add signal is sent to a Pipe during a simulation, the specified amount of mass of each species in the discrete change vector is added to pathway. If the Source Zone Length is zero (the default), the mass is applied at the beginning of the Pipe. If the Source Zone Length is greater than zero, the mass is distributed uniformly over the specified length.
Note: The discrete change
vector cannot contain negative numbers (i.e., you can NOT discretely remove mass
from a Pipe; you can only add mass).
Like most input fields that accept discrete change signals, you can specify multiple discrete changes. You can do this in two ways:
1. You can enter multiple discrete changes into the input field by separating the entries using a semi-colon; and
2. You can use the Multiple Discrete Changes button to the right of the input field (i.e., the small button with two exclamation marks) to access a table listing the Discrete Changes (to which you can add or delete entries).
In the latter case, any Discrete Changes which are added to the list are also automatically added to the input field, separated by semi-colons.
The Discrete Changes field can be very useful for instantaneously modifying your system in response to discrete events. Note, however, that this feature should be used with care, since when it is applied, conservation of mass in the system is the responsibility of the user.
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