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Welcome to the GPS-X Slideshow! This slideshow presents many of the
powerful features of GPS-X, and demonstrates how a GPS-X layout is
developed from start to finish. Please take a few moments to work through
the slideshow; alternatively, you may wish to wait for all of the images
to load and then print out a hard copy of the slideshow so that you may
review it at your leisure. Slide 1: The GPS-X Drawing Board
This is GPS-X's main window. It contains GPS-X's main menu bar (the
buttons labelled "FILE", "VIEW", "BUILD", etc., are drop-down menus which
each contain several GPS-X commands); it also contains buttons which bring
up other windows (the "LOCATOR" and "PROCESS TABLE" buttons) as well as
buttons which modify the drawing mode (the "REPLACE", "DELETE", "MOVE",
"REVERSE", and "BLOCK" buttons). The large area below this row of buttons is GPS-X's "drawing
board"; the layout of the treatment plant to be modelled is created here.
For this slideshow, we will be building a layout representing a
treatment plant with both primary and secondary treatment; the secondary
treatment will be carried out using the activated sludge process, using
two parallel liquid trains. The first step is to bring up the GPS-X Process Table; this is a
window which contains all of the objects available in GPS-X (see Slide 3
for a labelled close-up of the Process Table). From the Process Table,
objects can be selected and placed on the drawing board. In this slide, we
have placed an influent object on the drawing board. The "LOCATOR" window can be used to select an area of the drawing
board for viewing. Here we have selected an area large enough to hold our
completed layout.
The GPS-X Process Table contains allows easy access to all of the
objects supported by GPS-X. To place one of these objects on the drawing
board, the user simply selects the desired object with the mouse, and then
clicks on the desired location of that object in the drawing board.
*The acronyms used in this figure are defined below:
Several objects have been added to the layout. At the far left is
the influent object, which represents the influent entering the plant. To
the right of the influent object is a pump object; this will allow
by-passing of the plant during very high influent flow conditions. To its
right is a combiner object, followed by a primary clarifier. Two liquid
trains have also been added, each containing a plug-flow reactor object
(representing an aeration tank) and a secondary clarifier.
Several objects have been added to the layout. To the right of the
influent object at the far left is a pump object; this will allow
by-passing of the plant during very high influent flow conditions. To its
right is a primary settler, followed by a splitter object. Two liquid
trains have also been added, each containing a plug-flow reactor object
(representing an aeration tank) and a secondary clarifier.
The layout of the plant has been completed: several objects have
been added, and the connections between the objects have been defined --
all accomplished with just a few clicks of the mouse. The only new object
type is the right-most object in the layout, which is an effluent object
representing the effluent discharge point. The new objects are at the far
right in the layout: an effluent object representing the effluent
discharge point, and two combiner objects.
Once the layout has been completed, it is necessary to define which
models are to be used for the objects in the layout. For example, the user
can choose from one of three possible models for the influent object:
The model for the secondary clarifier in the first (topmost) liquid
train is being defined. The user can choose from several settling models,
including reactive and non-reactive models, as well as one-dimensional and
two-dimensional models.
After models have been assigned to each of the objects, the next
step is to define the necessary parameters. For the plug flow reactor
object, the following types of parameters can be set:
A form such as this one allows the user to enter the model
parameters. This form allows the kinetic parameters of the plug flow
reactor to be set; additional parameters can be accessed using the "NEXT"
button. The values shown here are the default values for the kinetic
parameters of the plug flow reactor object. The check marks in the squares to the left of the first two
parameters indicate that we intend to manipulate these parameters during
the course of a simulation. (The check marks are placed here as an example
only; we do not actually want to manipulate these parameters for this
example.)
In this example, we want to be able to control the influent flow
rate as the simulation progresses. The required steps are:
Once the controller has been defined, it can be displayed with the
"SHOW" item of the "CONTROLS" menu. This slider allows the user to manipulate the flow between 0
m3/day and 10,000 m3/day; this is done by dragging
the handle of the slider with the mouse. The number to the left of the
slider represents the current value of the slider.
This slide shows the different types of controls that can be
defined. (Please note, however, that the controls shown here are not used
in this example, with the exception of the influent flow slider).
On/off controls are often used for activating and deactivating
automatic controllers; the on/off control shown in this slide controls the
operation of the automatic dissolved oxygen controller. The "controller type" control is a drop-down control. Available
options for the "controller type" variable are P, PI, and PID; this
control allows the user to select from these options. The "DO Setpoint" control is an up/down control; the value of the
dissolved oxygen setpoint can be incremented or decremented by clicking on
the left and right arrows, respectively.
Each object has a number of "display variables" that can be placed
on various types of graphs. Here, we wish to place the dissolved oxygen
profile on a graph, so we need to display the "state variables" dialog
(since dissolved oxygen is a state variable).
The steps required to complete our graph of the dissolved oxygen
profile are:
Also note that there are several types of graphs available to the
user; these are:
GPS-X's DEFINE command can be used to define parameters which are
not related to any particular object or model, but rather are "plant-wide"
in scope. One such variable which is used frequently in wastewater
engineering is the solids retention time (SRT), which is selected above.
Other variables which can be defined with this command are:
Once the layout has been completed and the desired controls and
displays have been defined, it is necessary to compile the model in order
to simulate the plant. Normally, this can be done in one step by clicking
on the "BUILD" button; however, in certain special situations the code and
the executable files must be generated separately, as shown above.
Normally, for models of moderate size, the compilation step takes
only one or two minutes.
Once the model has been compiled, simulations can be run from the
"SIMULATION CONTROL" window. "Scenarios" can also be defined from this
window. In GPS-X, a scenario is simply a list of commands that are
recorded when you make changes to the object data entry forms.
Saving a scenario stores these commands for later retrieval; running the
scenario involves the playback of these instructions.
Here, we have defined a "Demo Run" scenario, in which we have
modified the influent flow rate and the wastage flow rate in the plug flow
reactors.
Often, it is desired to run the model to steady-state before
performing dynamic simulations. In GPS-X, this is done by checking the
"STEADY STATE" box and then starting the simulation. Here, the
steady-state simulation has achieved 100% convergence, as indicated by the
"CONVERGENCE" bar in the lower-right corner of the "SIMULATION CONTROL"
window.
This slide shows a one-day simulation in progress. The graph in the
upper-right corner shows the influent flow rate (in red) as well as the
effluent suspended solids (in blue). The histogram in the lower-right
corner shows the instantaneous dissolved oxygen profile in one of the plug
flow reactors. The influent flow rate has been modified from its initial value by
manually adjusting the position of the slider in the upper-left corner.
Suppose that you had both influent flow rate data and effluent
suspended solids data for a real plant. In order to calibrate the model,
you would need to be able to compare the simulation's output variables of
interest (here, effluent suspended solids) for a simulation which uses the
same time-varying inputs as your real plant (here, influent flow rate).
In GPS-X, this is easily accomplished: the influent flow rate
controller can be defined as a "file-input" type controller, meaning that
it takes data from an external data file. Effluent suspended solids data
can be displayed automatically alongside the simulation results; the data
is plotted as plusses ("+") while the simulation results are continuous
lines. The case in this slide is obviously synthetic; it has been created
from the saved results of a previous simulation, which was then re-run
with slight modifications to the secondary clarifier's settling
parameters. However, it demonstrates the ease with which GPS-X can be used
to develop calibrated models.
Often, it is necessary to determine the sensitivity of the model's
results to fluctuations in certain parameters -- for example, to obtain a
measure of the error in the model's predictions. This can be easily
accomplished with the GPS-X's ANALYZE Tool. Here, we will set up a
steady-state sensitivity analysis of the mixed liquor suspended solids to
the wastage flow rate from the plug flow reactor.
This slide shows the results of the completed sensitivity analysis.
Graphs of this type can be used to determine the amount of wastage
necessary to achieve a desired level of MLSS.
The GPS-X OPTIMIZER can be used to automate many of the tedious
tasks required to calibrate a model. In this slide we are simultaneously
optimizing the value of two parameters which control the kinetics of the
biological reactions in a batch reactor. The OPTIMIZER will find the
values of the parameters which results in the best possible fit betwen the
simulated soluble substrate values and those supplied in an external data
file. This is the end of the GPS-X slideshow. While we have covered many
of GPS-X's features, GPS-X has many more powerful features that make it
the best wastewater treatment plant simulator available. Examples of
features not covered in this slideshow include:
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