Monster Media 1996 #14/Monster Media No. 14 (April 1996) (Monster Media, Inc.).ISO/business/mixing10.zip/NETWORK.TXT

Text File | 1992-01-03 | 21KB | 455 lines

                          INTRODUCTION


There are two program files provided on the disk.  The program
named NETWORK.EXE is designed to work on IBM compatible computers
that are limited to 640 Kbytes of memory.  The program called
NETEXP.EXE  will work on IBM compatible computers that have
EXPANDED memory.  A driver is required ( such as LIM-386 ) in your
CONFIG.SYS file to enable the program to use the upper memory of
your computer.  The NETEXP program can use up to 8 Mbytes of
expanded memory to handle networks with over 2000 pipes.  The basic
network program is limited by memory to systems of less than 1000
pipes.

The programs work best on systems with hard disks, since the
programs makes use of frequent disk operations to read in the
various screens in the program.

To install the programs simply copy all the files on the disk to a
subdirectory of the hard disk.  The files with extensions PIC and
INP are required as well as the EXE files for the program to
operate.

                        NETWORK ANALYSIS


Large complex networks of pipes and pumps are a common feature of
many chemical plants, both for the distribution of process streams
and utilities such as cooling water.  Large networks also are found
in the petroleum, natural gas, and water distribution systems.

A pipe network consists of groups of pipes and piping components
that are joined together at Nodes.  The network can consist of
loops typical of water distribution systems or highly branched
systems typical of flare systems.

It is of interest to calculate the steady state behavior of the
network under various conditions of output flowrates, pump pressure
heads etc.  The solution of pressure drop in a single phase line is
simple, but pipe networks are extremely difficult to solve by hand
techniques due to the iterative nature of determining the
interactions of the flow on various upstream and downstream loops
and branches.

The problem consists of determining  all unknown Node pressures and
pipe flow rates given the information known about the network.
This information consists of the layout of the pipe network
including the manner in which the pipes are connected.  The pipes
diameters, and length.  All fittings on the pipes.  The
charactistics of pumps in the system.  And all known flows and
pressures that are fixed at specified Nodes.

The first attempts on this problem were based upon the Hardy Cross
method.  In the precomputer days the Hardy Cross method was used.
This method applied Newtons method considering individual loops of
piping and laboriously solving them one equation at a time until
convergence was reached.  This method was generally slow and
frequently did not work.

The method used in this program is based upon Newton-Raphson
techniques with internal correction factors applied to improve
convergence.  The Newton-Raphson approach is the fastest method to
achieve solution, but it requires a reasonably accurate estimate of
the initial pressure profile in the network to arrive at a
solution.

Consequently, the network program will  estimate the unknown node
pressures from the information supplied for fixed node pressures
and flow rates.



                        PROGRAM OPERATION


The most important work needed to operate this program is done with
the computer off.  It is first necessary for you to sketch up the
network that you wish to solve before using the computer.  This
sketch must show all pipes and nodes and all the nodes and pipes
must be numbered.  The sketch should also show elevations if a
liquid system with varying grade levels is to be solved.  The
sketch should show all pumps, fittings, control valves and other
known pressure drops.  All flows into and out of NODES should be
shown if they are to be specified.  All pressures to be specified
should be added to the sketch.  This sketch should be as neat and
complete as possible, particularly for a large network, since
errors and extensive changes may require the network to be
reentered.  An approximate guesstimate of the pressure profiles for
the various nodes should be made.  The program can generate its own
initial guesses however from limited information on fixed
pressures, however the users estimates will be used when provided.


The program is started from the hard disk by typing the name of the
program NetWork.EXE from the DOS command line.  If the Expanded
Memory version is to be used type the name NETEXP.EXE at the DOS
command line.

The program will load and the Main Menu screen will be shown on the
monitor.  The various features of the program are addressed by
pressing the command keys F1 to F10 from the main menu.  The
programs operation is terminated by pressing the ALT key followed
by the Q key.

                            MAIN MENU

     F1   HELP                               F2   INPUT FLUID DATA

     F3   INPUT PIPE DATA                    F4   INPUT NODE DATA

     F5   REVIEW INPUT DATA                  F6   REVIEW RESULTS

     F7   NEW PROBLEM                        F8   PRINTER OPERATION

     F9   DISK OPERATIONS                    F10  RUN PROGRAM


                      ALT Q = QUIT PROGRAM







The function of the various keys are described as follows:


F1   The F1 key will show a help screen that give a
          abbreviated instructions to the program.

     F2   The F2 key is used to input the general physical
          properties of the fluid that flows through the lines.

     F3   The F3 will input the Pipe information

     F4   The F4 key will input the Node information

     F5   The F5 key will allow you to review a summary of the
          input information.

     F6   The F6 key will review a summary of the results for both
          Nodes and Pipes.

     F7   The F7 key will erase all information on the network and
          allow you to run a new case.  Save the data before
          pressing the F7 key.

     F8   The F8 key will print out the input or results of the
          network calculation

     F9   The F9 key permits disk operations such as saving the
          network input data, Loading a new data set from the
          directory or changing the directory.  The network data
          should be saved before printing the data.

     F10  The F10 key will run the program to solve the  network.
          It is recommended that the input data be saved before
          running the program.



                           FLUID INPUT

After you have pressed the F1 key a window will pop up that will
request that you press either the F1 key to select a liquid or the
F2 key to input the gas properties.  The program will work with
either liquids or gases, but not both.  If the F1 key was pressed
then a window will pop up requesting that you input the liquids
density in Lb/Ft3 and the viscosity in Centipoise.  If the F2 key
was pressed a window will pop up that requests the Molecular
Weight, Temperature, Viscosity in Centipoise, the Compressibility
factor Z  and the K ratio (Cp/Cv) of the gas.  The fluid properties
can also be altered for each line on the pipe input section of the
program, but these general properties must be added first.  This
step is the first activity that you need to perform in inputting
the problem description.

                         PIPE INPUT DATA

The F3 key is pressed to input the pipe data.   The pipe input
screen will come on the monitor and request the total number of
pipes to be input.  After you give the total number of pipes the
cursor will move to each field to be filled in for the first pipe
in the network.  After all the input data is filled in for the
first pipe, press the F4 key to proceed to the next pipe.  The
pipes are numbered automatically by the program.  If you wish to
edit a previously filled in pipe then press the F3 key to go
backwards.  It is possible to move rapidly to a specified pipe for
editing by pressing the F1 GOTO key.  This is useful for large
networks.  You can move rapidly through various fields on the pipe
input screen by using the up and down arrow keys.

For a given pipe it is necessary to input the following data
otherwise the program will fail in execution.
Required information includes the entering node and exit node, as
well as descriptive data on the pipe such as the nominal diameter,
pipe length, and pipe roughness. Other information such as fittings
and check valves etc. is optional but needed to obtain accurate
results.

The node numbers in and out give the direction of flow in the pipe.
Flow in the pipes from the inlet node to the outlet node is a
positive number in the network solution.  The order of the node
numbers is arbitrary except if a pump, check valve or flow
controller is included in the pipe description.  In this case, it
is necessary to give the correct direction of flow.  The pipe
internal diameter are automatically provided by the program from
the pipe schedule selected when the nominal diameter is filled in.

PIPE SCHEDULES..F2 KEY
Different pipe schedules can be selected by pressing the F2 key. If
the F2 key is pressed then a screen is shown that offers several
selections of standard schedules.  Select the one you want by
entering the number corresponding to it.  The schedules can be
selected for each individual pipe.  The standard schedule if none
is selected from the menu is SCH 40.  The pipe roughness is also
provided for new C.S. pipe from the pipe schedule.  This value can
be overridden by the user.

FITTINGS.. F5 KEY
If the F5 key is pressed then a screen will come up that gives the
equivalent feet (L/D) for several common fittings.  These values
were taken from the Crane manual.  You select the fitting by
inputting the number of fittings followed by pressing the enter
key.  The arrow keys will rapidly move the cursor to the different
fittings.      The fitting screen can be printed out by pressing
the F9 key.  Return to the pipe input screen by pressing the F10
key.  The number of equivalent feet will be shown on the pipe
screen for the fittings described.

Additional pressure drop in the line in PSI can be specified to
simulate a control valve or heat exchanger or other obstruction in
the line.  It is also possible to specify a flow regulator in the
line to limit the flow to a specified maximum GPM.  However, The
flow controller option can cause convergence problems and it is
recommended to first solve the network without a flow controller to
assist in generating good pressure estimates.  Expect that the
number of iterations will be considerably increased if the flow
controller option is selected.

The physical properties of the fluid in the pipe as specified in
the general fluid input option are shown on the screen.  You may
override these values by inputting different values for density, or
viscosity etc. and the program will use them when calculating this
line.  Do NOT input gas properties on liquid flow problems or vice
versa.

CHECK VALVES..F6 KEY
Check valves can be specified by pressing the F6 key.  If the line
has a check valve then the inlet and outlet node numbers must be
correctly specified.  The is no flow possible against the check
valve.

PUMP..F7 KEY
If a pump is to be specified then only the inlet and outlet node
should be specified.  The length and diameter terms have no meaning
in a pump specification and will be ignored by the program.  The
pump outlet pipe should be connected to the pump node out
specification.  The pumps A & B values are calculated by the
program by pressing the F7 key.  A screen will come on the requests
information on the pump curve, specifically the GPM and Pump
discharge pressures.  At least 3 points, and a maximum of 10 points
must be specified for the program to calculate the A & B values for
the equation Pout = A - B*GPM^2.  Press the F1 key to calculate the
coefficients and to see the calculated pressure values for the
input flow.  When you press the F10 key to return the A & B values
will be entered on the pipe screen.

DELETE..F8 KEY
The F8 key will delete a the pipe that is shown on the screen, and
all downstream pipes will be renumbered.

ADD PIPES..F9 KEY
The F9 key will allow you to add additional pipes to the network
beyond the number originally specified.  The new pipes will be
added at the end.







                        NODE INPUT F4 KEY


Pressing the F4 key from the Main Menu will bring up the node input
screen.  The first field to be inputted is the total number of
nodes in the network.  The total must be inputted followed by the
return key.  The program then requests the following information
for each Node.  After all the Node information is filled in press
the F4 key to proceed to the next node.  The editing features for
Node input is the same as for the Pipe Input screen.

The Elevation of the node is relative to a arbitrary grade level.
This is important for liquid flow problems if hydrostatic head is
to be considered in the pressure drop calculations.

The pressure of the node in PSIA for gases, PSIG is satisfactory
for liquids.  Reasonably accurate pressure estimates are needed for
the network to converge.  Pressures are required if the pressure at
the node is to be specified, for example where the main liquid flow
into the network enters, or at exit points.  To Specify if the
pressure is to be fixed at the Node press the F1 key.  The F1 key
is a toggle switch, and can be used to convert pressure estimates
to specified pressures and vice versa.

Additional nodes can be added to the network by pressing the F5
key.  There is no provision to delete a node because this can cause
considerable changes to the network since the pipes would be
changed.  If a node is to be deleted it will be necessary to
reinput the network.

The Liquid rate into or out of the node is given if a specific
value is to be specified.  Flows into the Node are entered a
positive numbers.  Flows out of the node are entered as Negative
Numbers.

The units for flow can be changed by pressing the F2 key.  A
selection window will pop up and offer alternative flow values such
as GPM, LB/H, or ACFM.  Only one set of units may be used for the
program.  They cannot be mixed.  The program will use the last
selection made, the default value is GPM.

                       REVIEW INPUT F5 KEY

The F5 key from the Main Menu will bring up the review input
screen.
There are two active windows on the screen.  The top window gives
the Pipe Input data, and lists the pipe number, Nodes in and out,
and other data such as the pipe diameter, length, Roughness, and
pump Constants if selected.  The window will scroll down or up to
the limit of the data by pressing the Arrow keys.

The lower window give the Node Input Data.  It lists the Node
number, Node specification ie. Estimated pressure, Specified
Pressure or Pumped ( If a liquid flow rate in or out was
specified).
The elevation of the Node and the Flow rate in the selected units
is also shown.  This window will also scroll by using the arrow
Keys.

The Function Keys F1 and F2 are used to pick the desired window to
scroll to review the input.  Initially the Pipe window is
specified.
After reviewing the input you can return to the main menu by
pressing the F10 Key.

                         DISK OPERATIONS

Press the F9 key from the main menu to perform disk operations.
Once you press this key a message is shown on the screen to press
either the F1 Key to save the input data, or The F2 key to read in
a new file from the disk, or the F3 key to change the default
directory.  The F3 key can by used for example to save the data to
a different subdirectory or floppy disk if you do not wish to use
the directory that the program was booted up from.

Be careful to save the input data on the network as your first
operation to prevent possible running problems from causing the
data to be lost.  Do not accidently press the F2 key if you intend
to save the data because reading in a new file will cause the input
data to be lost.

If you are saving the data by pressing the F1 key a screen will
come on requesting the name of the file.  Input a maximum of 8
characters per the DOS convention, and do NOT add a period or
extension to the name, Network data files are automatically given
the extension NET by the program.  Do NOT use a prefix for sub
directories here.  The F3 key is to be used for setting the default
sub directories.

If you are loading in and existing data set, Press the F2 key.  A
selection window will come up that lists the files on the disk that
have the extension NET, and are network data files.  The file to be
loaded is selected by using the arrow keys to move the colored box
to the selected file and then press the return key to load in the
file.


                     RUNNING THE PROGRAM F10

The program is run by pressing the F10 key.  This should be done
after a problem has been loaded from the disk, or after the data
has been completely inputted, checked, and saved to the disk.

While the program is running a window will pop up that gives the
number of the iteration and the sum of the residuals squared for
the programs convergence.  The network will iterate to reach a
convergence tolerance of 0.001 or for a maximum of 200 iterations.

Small networks with less than say 10 pipes will usually converge
very rapidly in less than 10 iterations.  Large networks can take
considerably longer.  This window will let you watch the progress
of the solution.  If the residuals do not converge to zero then the
solution is not accurate.  If there is something wrong with the
problem statement and convergence is not possible then a warning
message will appear and the convergence routine will stop, and
return you to the main menu.



                       REVIEW RESULTS  F6

After the program has been run, the results can be reviewed by
pressing the F6 key.  The Result screen is similar to the Review
Input screen and works in the same manner.  The Pipe Data results
are scrolled by pressing the Arrow keys. and the Node Data can be
selected by pressing the F2 key.

The pipe results for each pipe are the Flow in the pipe, the
velocity, calculated friction factors and Reynold's Numbers,
Average Density of the fluid in the pipe, the Head Loss in PSI
across the pipe ( Head Loss includes additional Pressure drops and
Static head differences ) and the Pump Head of and Pumps in PSI.
Negative number for Flow or Velocity indicate that the flow in the
pipe is from the outlet to the inlet node specified.

The Node Results give the pressures at each Node calculated, the
Nodes Elevation and the Flows Into or Out of the Node.  Flows Out
are Negative Numbers, Flows In are Positive.  These flows are
obtained by performing material balances at each node.  Small
numbers like 0.01 GPM indicate convergence tolerances.  The flow
result at a Node should be zero unless the node has a Flow or
Pressure specified.  Fixed pressures indicate locations where flow
is either entering or exiting the Network.

                    PRINTER OPERATIONS F8 KEY

The Printer should be On and connected to the computer before
pressing this key.  A window will pop up that gives you the option
to print out the Input, Print the Output or to give a line feed or
Form Feed to the printer.  Press the Function key shown in the
window to select the case.  The Printer option assumes that the
printer is a continuous feed printer such as an Epson.

                       NEW PROBLEM F7 KEY

If you press the F7 key a message will appear to confirm that you
wish to wipe out the existing network from the computer memory and
start a new problem.  If you have not save the data file you should
answer the question by typing the N key for No.  Type a Y to start
a new problem.

                      QUITTING THE PROGRAM

The program is terminated by pressing the ALT key and
simultaneously pressing the Q key from the Main Menu.  A message
will appear asking for confirmation that you wish to quit.  Press
the Y key to answer yes and the program will shut off.