Fathom 7.0 Modules Guide SI

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AFT Fathom

Modules Users Guide

AFT Fathom version 7.0 Modules

Incompressible Pipe Flow Modeling

Applied Flow Technology


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CAUTION!AFT Fathom is a sophisticated pipe flow analysis program designed forqualified engineers with experience in pipe flow analysis and should notbe used by untrained individuals. AFT Fathom is intended solely as anaide for pipe flow analysis engineers and not as a replacement for otherdesign and analysis methods, including hand calculations and soundengineering judgment. All data generated by AFT Fathom should be

independently verified with other engineering methods.

AFT Fathom is designed to be used only by persons who possess a levelof knowledge consistent with that obtained in an undergraduateengineering course in the analysis of pipe system fluid mechanics andare familiar with standard industry practice in pipe flow analysis.

AFT Fathom is intended to be used only within the boundaries of itsengineering assumptions. The user should consult the Users Guide for adiscussion of all engineering assumptions made by AFT Fathom.

Information in this document is subject to change without notice. No part of this UsersGuide may be reproduced or transmitted in any form or by any means, electronic ormechanical, for any purpose, without the express written permission of Applied FlowTechnology.

2008 Applied Flow Technology Corporation. All rights reserved.

Printed in the United States of America.

First printing.

AFT Fathom, AFT Mercury, Applied Flow Technology, and the AFT logo are

trademarks of Applied Flow Technology Corporation.

Microsoft, Visual Basic, Excel and Windows are trademarks or registered trademarks ofMicrosoft Corporation.


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Contents

Summary

1. Introduction .................................................................... 1

2. Using Goal Seek and Control........................................ 7

3. Goal Seek and Control Example ................................. 33

4. Modeling Extended Time Simulation.......................... 47

5. Modeling Time and Event Based Transients ............. 81

6. Extended Time Simulation Example........................... 91

7. Working with Cost Databases................................... 113

8. Performing Cost Analysis.......................................... 137

9. Cost Analysis Example .............................................. 151

10. Using Modules Together.......................................... 169

Glossary.......................................................................... 179


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Table of Contents v

Detailed Contents

Summary..................................................................................................iii

Detailed Contents ..................................................................................... v

1. Introduction .................................................................... 1

What this users guide covers................................................................... 1

Modeling capabilities ............................................................................... 2

GSC module ....................................................................................... 2

XTS module ....................................................................................... 2

CST module ....................................................................................... 2Who can use AFT Fathom........................................................................ 3

Getting started with the AFT Fathom Modules........................................ 3

GSC module ....................................................................................... 3

XTS module ....................................................................................... 3

CST module ....................................................................................... 3

Using Modules together ..................................................................... 3Example models ................................................................................. 4

Using online help...................................................................................... 4

Activating modules................................................................................... 4

Opening models with and without module data ....................................... 5

Opening models without module data in a module............................ 6

Opening models with module data without an active module ........... 6Using modules in scenarios ......................................................... 6

2. Using Goal Seek and Control........................................ 7

What is the GSC module? ........................................................................ 7

How does the GSC module work?............................................................ 7

Using the GSC module ............................................................................. 8


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Enabling GSC use..................................................................................... 9

Goal Seek and Control Manager ............................................................ 10

GSC variables ......................................................................................... 11Types of variables...................................................................... 11

Creating and deleting variables ................................................. 12

Applying variables..................................................................... 14

Object type................................................................................. 14

Junction type.............................................................................. 14

Junction number and name........................................................ 14Variable parameter .................................................................... 14

Linking variables ....................................................................... 15

Variable bounds......................................................................... 15

Reviewing junction input data................................................... 15

Editing junction input data ........................................................ 15

GSC goals ............................................................................................... 16Types of goals............................................................................ 16

Creating and deleting goals ....................................................... 19

Applying goals........................................................................... 20

Goal types.................................................................................. 20

Object types ............................................................................... 21

Reviewing object input data ...................................................... 21

Editing object input data............................................................ 21

GSC data in Model Data......................................................................... 22

GSC feedback during the solution.......................................................... 22

GSC data in output ................................................................................. 23

Changing input values to GSC results.................................................... 24

Transferring results to initial............................................................ 24

Generating a disconnected scenario................................................. 25

When goals cannot be achieved.............................................................. 26

Physically unrealistic goals.............................................................. 27

Better starting point needed ............................................................. 27

Changing control parameters ........................................................... 27

Changing tolerance in Solution Control .................................... 28


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Table of Contents vii

Changing goal seeking numerical control ................................. 29

What to do if the Solver gets stuck......................................................... 29

GSC data differences across scenarios ................................................... 32

3. Goal Seek and Control Example ................................. 33

Topics covered........................................................................................ 33

Required knowledge............................................................................... 33

Model file ............................................................................................... 34

Problem statement .................................................................................. 34

Step 1. Start AFT Fathom....................................................................... 34

Step 2. Specify system properties........................................................... 34

Step 3. Build the model .......................................................................... 35

A. Place the pipes and junctions ................................................ 35

B. Enter the pipe data................................................................. 36

C. Enter the junction data .......................................................... 36

J1 Reservoir ............................................................................... 36

J9 Reservoir ............................................................................... 36

J3 Tee......................................................................................... 37

J6 Elbow .................................................................................... 37

J4, J7 Control Valves................................................................. 37

J5, J8 Heat Exchangers.............................................................. 37

J2 Pump ..................................................................................... 37

D. Check if the pipe and junction data is complete ................... 38

Step 4. Open the Goal Seek and Control Manager................................. 38

Step 5. Add a variable............................................................................. 39

Step 6. Add a goal................................................................................... 40Step 7. View GSC settings in Model Data ............................................. 43

Step 8. Enable goal seeking.................................................................... 44

Step 9. Run the model............................................................................. 44

Step 10. Examine the results................................................................... 45

Analysis summary................................................................................... 46


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4. Modeling Extended Time Simulation.......................... 47

What is the XTS module?....................................................................... 47

How does the XTS module work?.......................................................... 48

Using the XTS module ........................................................................... 48

Enabling XTS transient mode................................................................. 49

Transient control window....................................................................... 51

Entering junction transient data ....................................................... 52

Initiating transients .................................................................... 53

Repeat transient ......................................................................... 53

Transient Special Conditions..................................................... 53

Entering reservoir volume data............................................................... 54

Infinite reservoirs ............................................................................. 54

Finite reservoirs................................................................................ 54

Finite open tanks........................................................................ 55

Finite closed tanks ..................................................................... 55

Known parameters initially.............................................................. 57

Entering reservoir transient data ...................................................... 58

Infinite reservoirs....................................................................... 58

Finite open tanks........................................................................ 58

Finite closed tanks ..................................................................... 59

What happens when finite tanks overflow? ..................................... 59

What happens when finite tanks drain? ........................................... 60

What happens when pipes are uncovered? ...................................... 60

Interpreting pipe depth and elevation data....................................... 61

Maximum and minimum pressures in closed tanks ......................... 61Transient data in Model Data window ................................................... 61

Solution progress window with XTS ..................................................... 62

Transient control difference methods..................................................... 63

Forward difference method.............................................................. 64

Central difference method................................................................ 64

Relative and absolute tolerance ................................................. 65Relaxation.................................................................................. 67


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Table of Contents ix

Maximum iterations................................................................... 67

Changing parameters during the run ......................................... 67

Output values displayed with forward difference............................ 67Output values displayed with central difference.............................. 68

Transient data in Output window ........................................................... 69

Detailed results for a time step......................................................... 69

Transient results for all time steps ................................................... 69

Quick graphs .................................................................................... 70

Transient Graph Results ......................................................................... 73Profile graphs ................................................................................... 73

Animation of output................................................................... 74

Transient graphs............................................................................... 75

Transient Visual Report.......................................................................... 76

Special conditions................................................................................... 77

Special conditions with no transient data .................................. 77Special conditions with transient data....................................... 78

Pump special conditions ............................................................ 79

Transient Special Conditions ........................................................... 80

5. Modeling Time and Event Based Transients ............. 81

Time-based transients ............................................................................. 81

Event-based transients ............................................................................ 82

Single event transients ..................................................................... 82

Dual event transients: cyclic and sequential .................................... 83

Cyclic events.............................................................................. 83

Sequential events ....................................................................... 84Junctions with inherent event logic ........................................................ 85

Check valve...................................................................................... 86

Relief valve ...................................................................................... 86

Thought experiment to further clarify event transients .......................... 86

Other transient features........................................................................... 87

Absolute vs. relative transient data .................................................. 87Repeat transient................................................................................ 87


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Add time offset................................................................................. 87

Graphing the transient data .............................................................. 87

Event messages....................................................................................... 89Transient indicators on the Workspace .................................................. 89

Transient data in Model Data ................................................................. 90

6. Extended Time Simulation Example........................... 91

Topics covered........................................................................................ 91

Required knowledge............................................................................... 91

Model file ............................................................................................... 92

Problem statement .................................................................................. 92

Step 1. Start AFT Fathom....................................................................... 92

Step 2. Specify system properties........................................................... 92

Step 3. Build the Model.......................................................................... 93

A. Place the pipes and junctions ................................................ 93

B. Enter the pipe data................................................................. 93

C. Enter the junction data .......................................................... 94

J1 Reservoir ............................................................................... 94

J11, J13, J15, J17, J19 Assigned Pressures ............................... 95

J10, J12, J14, J16, J18 Valves ................................................... 95

J4, J6 Valves.............................................................................. 95

J3, J5 Pumps .............................................................................. 95

J8 Control Valve........................................................................ 96

J2, J7, J9 Branches .................................................................... 96

D. Check if the pipe and junction data is complete ................... 96

Step 4. Specify transient output time units............................................. 96

Step 5. Select transient analysis.............................................................. 97

Step 6. Open transient control ................................................................ 97

Step 7. Set up the system transients........................................................ 99

A. Auxiliary pump J5 transient. ....................................................... 99

B. Valve J6 Transient..................................................................... 100

C. Valve J12, J14, J16, J18 Transients .......................................... 100Step 8. Run the model........................................................................... 101


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Table of Contents xi

Step 9. Examine the transient results.................................................... 102

Analysis summary................................................................................. 111

7. Working With Cost Databases .................................. 113

Sources of cost data supported ............................................................. 113

Types of databases supported............................................................... 113

Engineering and cost databases ............................................................ 114

Cost Database window ......................................................................... 114

One time vs. recurring costs........................................................... 115

Creating cost databases......................................................................... 116

Pipe material costs ......................................................................... 118

Non-recurring costs ................................................................. 119

Recurring costs ........................................................................ 119

Junction costs ................................................................................. 119

Deleting costs................................................................................. 119

Non-recurring costs, non-pumps and control valves ............... 119

Recurring costs, non-pumps .................................................... 120

Pump and control valve costs .................................................. 121

Costs for tees and branches ..................................................... 122

Pipe fitting & loss costs ................................................................. 122

Scale tables..................................................................................... 123

Global multipliers in cost database ................................................ 124

Global multipliers in Database Manager ....................................... 124

Using cost databases............................................................................. 125

Database Sections.................................................................... 126

How repetitive costs are handled ................................................... 126

Using the Database Sources tables................................................. 127

Pipe costs in Pipe Specifications window...................................... 127

Cost for pipe fittings & losses........................................................ 130

Junction costs in Junction Specifications window......................... 131

All databases vs. selected cost databases....................................... 132

Cost Settings window..................................................................... 133Database locations in General Preferences .......................................... 134


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Reviewing application of cost data....................................................... 135

8. Performing Cost Analysis.......................................... 137

What is the CST module?..................................................................... 137

How does the CST module work?........................................................ 137

Using the CST module.......................................................................... 138

Accessing cost databases...................................................................... 139

Cost databases ................................................................................ 139

Energy Cost databases.................................................................... 139

Database Manager.......................................................................... 139

Cost Application Manager.................................................................... 139

Cost Databases ............................................................................... 141

Energy Cost Databases................................................................... 141

Cost Multipliers ............................................................................. 141

Maximum Cost Groups .................................................................. 141

Service Duration ............................................................................ 142

Cost Settings window ........................................................................... 142

Cost Calculations ........................................................................... 142

Energy Cost .................................................................................... 142

Cost Definitions ............................................................................. 143

Monetary vs. non-monetary costs .................................................. 143

Engineering parameter costs .......................................................... 144

Custom monetary units .................................................................. 144

Cost Time Period ........................................................................... 144

Cost Report ........................................................................................... 145

What are maximum cost groups? ......................................................... 146

Typical usage guidelines................................................................ 147

Creating a maximum cost group for pumps................................... 147

How cost multipliers are applied with maximum cost groups....... 148

Maximum cost is the base cost before multipliers are applied 148

Pump operates part of the time................................................ 148

Spare pump .............................................................................. 148Maximum cost groups for control valves....................................... 149


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Table of Contents xiii

9. Cost Analysis Example .............................................. 151

Topics covered...................................................................................... 151

Required knowledge............................................................................. 151Model file ............................................................................................. 152

Problem statement ................................................................................ 152

Step 1. Start AFT Fathom..................................................................... 153

Step 2. Open the model file .................................................................. 153

Step 3. Cost Settings............................................................................. 153

Cost Calculations ........................................................................... 154

Cost Definitions ............................................................................. 154

Cost Time Period ........................................................................... 154

Step 4. Create the cost databases.......................................................... 155

Create a new cost database for the pipe costs................................ 155

Enter the pipe material costs .......................................................... 156

Create cost scale tables .................................................................. 159

Add the costs for pipe fittings........................................................ 160

Create a new cost database for the pumps ..................................... 163

Enter the pump costs................................................................ 163

Connecting the cost databases........................................................ 164

Step 5. Including items in the Cost Report ........................................... 165

Step 6. Run the model........................................................................... 166

Step 7. Examine the Cost Report.......................................................... 166

Analysis summary................................................................................. 168

Cost optimization with AFT Mercury .............................................. 168

10. Using Modules Together.......................................... 169Model file ............................................................................................. 169

Problem statement ................................................................................ 169

Start AFT Fathom................................................................................. 170

Open the model file .............................................................................. 170

Variable and goal settings .................................................................... 170

Transient control settings ..................................................................... 170Junction transient data .......................................................................... 172


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C H A P T E R 1

Introduction

Welcome to the AFT Fathom7.0 Modules. AFT Fathom is a graphicalplatform for modeling incompressible flow in pipe networks.

There are three optional add-on modules which extend AFT Fathoms

extensive modeling capabilities into new areas. The Extended TimeSimulation (XTS) module allows the engineer to model time varyingsystem behavior. The Goal Seek & Control (GSC) module allows theengineer to perform multivariable goal seeking and simulate controlsystem functions. The Cost (CST) calculation module allows theengineer to calculate system costs, both initial and recurring. Themodules can be used individually or together.

The AFT Fathom Modules automate and organize a range of engineeringfunctions, bringing increased productivity to the piping system engineer.

What this users guide covers

This Users Guide documents features in the AFT Fathom Modules

which are not discussed in and are not part of the standard AFT Fathom7.0 Users Guide provided separately. This Users Guide assumes theuser is familiar with AFT Fathom. Please consult the AFT Fathom 7.0Users Guide for information on standard AFT Fathom functions.


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2 AFT Fathom 7.0 Modules Users Guide

Modeling capabilities

GSC module

Can automatically have parameters vary to meet specified goals

Can specify group goals to ensure a group of pipes or junctionssatisfies operating criteria

Can link variables to force commonality in solutions

Can easily apply and unapply goals and variables

XTS module

Can model transient behavior over time

Supports time and event transients for valve position, pump speed,

pump control setpoints, pressure or flow, reservoir liquid level orsurface pressure, spray CdA, control valve setpoints

Reservoirs can be finite with defined tank geometries so surfacelevel changes with time can be computed

Reservoirs can be open or closed. If closed, surface pressure changesdue to gas compression (when the liquid level changes) can bemodeled.

Transient data shown on Output window and controlled by specialOutput Control features

Transient data can be graphed over time

Profile data can be animated

Quick Graph on Output window shows a popup graph of transient

data

CST module

Can obtain cost for entire pipe system (has all cost capabilities ofAFT Mercury)

Can account for non-recurring and recurring costs


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Chapter 1 Introduction 3

If used with XTS module, can calculate pump energy usage and costover time

Who can use AFT Fathom

AFT Fathom assumes that the user possesses a good general knowledgeof engineering pipe system hydraulics. Even the most advanced andeasy-to-use software package cannot make up for a lack of fundamentalknowledge on the part of the user. The level of knowledge assumed by

AFT Fathom is consistent with that obtained in a typical engineeringundergraduate course in fluid mechanics. See the copyright page in thisUsers Guide for cautionary information.

Getting started with the AFT Fathom Modules

GSC module

Chapter 2 discusses in detail how to use the GSC module. Chapter 3focuses on an example application.

XTS module

Chapter 4 discusses in detail how to use the XTS module. Chapter 5discusses time and event transients. Chapter 6 focuses on an exampleapplication.

CST module

Chapter 7 discusses how Cost Databases are built and used. Chapter 8

discusses in detail how to use and apply data to generate costcalculations. Chapter 9 focuses on an example application.

Using Modules together

Chapter 10 discusses how the modules can be used with each other andlooks at an example.


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Example models

An auxiliary help file (called FathomExamples.hlp) is installed with

AFT Fathom and leads the user through modeling a number of realworld systems. This help file can be accessed by choosing ShowExamples from the Help menu. The example models discussed inFathomExamples.hlp are installed in the Examples folder. It can beopened from the Help menu by choosing Show Examples.

Using online helpTo access AFT Fathom's online help, press the F1 function key or selectHelp from the menu bar. For convenient access, much of the content ofthis Users Guide is included in the Help system. The Help button ineach dialog window provides context-sensitive help on the features ofthat window.

In the Help system you have the option of searching for information onspecific topics or searching through the hierarchical layout to find moregeneral information.

Activating modules

When AFT Fathom launches, the first window displayed is the ActivateModules window (Figure 1.1 top). This allows you to select whichmodules you would like to activate for use in AFT Fathom. If a license isnot found for a module, the selection will be disabled (Figure 1.1bottom). Even though the Activate Modules window allows you tochoose a module for activation, that does not mean that a license isavailable for use it just means that a license exists. If it is in use byanother user and thus not available for checkout, you will be informed

after clicking the OK button.

If there is a module you would like to always have activated when youstart AFT Fathom, select it in the Activate Modules window and thenclick the Set as Default button (see Figure 1.1).

If you do not want the Activate Modules window to display when youstart AFT Fathom, clear the Always Show check box provided.


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Chapter 1 Introduction 5

If, after starting AFT Fathom, you decide you would like to activate (ordeactivate) a module, you can open the Activate Modules window fromthe Options menu.

Figure 1.1 The Activate Modules window displays when AFTFathom launches, showing all modules available (top)or only some available (bottom).

Opening models with and without module data

What happens when you open a model that has module data withoutaccess to that module, and vice versa? This section discusses whathappens to the model.


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When AFT Fathom is used along with a module, that module is said tobe active.

Opening models without module data in a module

There is no problem opening a model without module data into AFTFathom when one or more of the modules is active. When doing so, themodel can be enhanced through the module features. However, once amodel which uses module features is saved, the data can only be retainedby continuing to use that model with the active module.

If you want to continue to use the original model without modulefeatures, you may want to keep two versions of the model. One for usewith modules and one without.

Opening models with module data without an activemodule

If you open a model which has module data in it, and that module is notactive, AFT Fathom will attempt to activate the module. If it cannot, themodule related data will not be displayed in AFT Fathom. Further, AFTFathom does not attempt to retain the original module data and it may belost if the model is later saved.

When you open the model in such cases, AFT Fathom will inform youwhat modules are used in the model, and warn you about lost data if you

open the model and save it. You will be given a choice to cancel themodel opening process at that point.

Important: Opening a model created with a module into an AFTFathom session without that module will usually result in the data beinglost.

Using modules in scenarios

You may have a model where some scenarios use certain modules whileothers do not. If a module is used in any scenario, AFT Fathomconsiders that entire model to be using the module. Thus even if thescenario which uses the module is not opened, the data may be lost whenthe model is saved.


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C H A P T E R 2

Using Goal Seek and Control

This chapter introduces the Goal Seek and Control Module (GSC).

Detailed information regarding GSC menus and functionality is given inthis chapter. Chapter 3 provides a detailed hands-on GSC example.

What is the GSC module?

Many engineering modeling tasks involve more than just directly solvinga system. In some cases a manual, cut and try method of changinginput variables to achieve desired operating results is required. When a

single parameter is being changed, the manual process (while tediousand time consuming) can be used successfully. However, varying two ormore parameters at the same time quickly becomes impractical.

The GSC module automates the process of changing input variables toachieve desired design goals. For single variable situations, the GSCmodule offers the advantage of being much faster than manual methods.Further, it provides a practical tool for solving cases when there are two

or more variables.

How does the GSC module work?

The GSC module employs numerical optimization technology like thatused in AFT Mercury. The optimization engine employed by the AFTFathom GSC module uses state-of-the-art optimization technologylicensed from Vanderplaats Research and Development, the leading


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company in optimization technology. However, rather than minimizingsome function value such as system cost or weight, the GSC modulesatisfies equality criteria using goal programming methods.

The core hydraulic solution in AFT Fathom is performed by theHydraulic Solver. In standard AFT Fathom usage, the Hydraulic Solveris called once to solve a system. The GSC modules NumericalOptimizer is used to call the Hydraulic Solver repeatedly, thus solving aseries of models with different inputs. The Numerical Optimizer adjuststhe user specified Variables (discussed later in this chapter) in orderforce the Hydraulic Solver output values to agree with the user specifiedGoals (also discussed later in this chapter). Figure 2.1 depicts therelationship between the different components.

Convergedon goals?

No

Yes

Numerical Optimizer

Hydraulic Solver

Graphical Interface

Input Output

Figure 2.1 The GSC module flowchart shows how the HydraulicSolver is called repeatedly in an iterative loop.

Using the GSC module

The user has the option of activating or not activating the GSC modulewhen AFT Fathom first loads. After AFT Fathom is loaded, the GSC

module can be activated or deactivated for use from the Options menu.Whether or not GSC is activated impacts the View menu, Analysismenu, Model Data window and Output window.

If the GSC module is active, the user can still run models without goalseeking. This is selected under Goal Seek & Control on the Analysismenu. Hence there are three possibilities for GSC.

1. GSC is not active

2. GSC is active and goal seeking is ignored


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Chapter 2 Using Goal Seek and Control 9

3. GSC is active and goal seeking is performed

Table 2.1 lists the three possibilities and the impact on various AFT

Fathom features.

Table 2.1 AFT Fathom feature accessibility based on GSCactivation and GSC use

GSC Not Active GSC Active GSC Active

Feature No Mode Ignore Use

"Goal Seek and Control

Manager" on View MenuNot Visible Visible Visible

"Goal Seek and Control" on

Analysis MenuNot Visible Visible Visible

"Goal Seek and Control" tab

in General Section of Model

Data

Not Visible Visible Visible

"GSC Variables" and "GSCGoals" tab in General Section

of Output window

Not Visible Not Visible Visible

Enabling GSC use

When the GSC module is active, two new menu items appear one onthe View menu and the other on the Analysis menu. On the Analysismenu is the Goal Seek & Control menu, from which the user can selectIgnore or Use.

The GSC module goal seeking is enabled by selecting Goal Seek &Control -> Use from the Analysis menu (Figure 2.2). This can beselected before or after a model is built. Pre-existing models built with

standard AFT Fathom can be opened with GSC and goal seeking dataadded.

Goal seeking can be turned off at any time by selecting Ignore from thesame menu. The Ignore mode causes the GSC module to function likestandard AFT Fathom. One difference is that users can still enter goalseeking data and this data is retained in the model. If the model isopened in standard AFT Fathom, this data will be lost. Table 2.1 relates

the differences between not using GSC and using it in Ignore mode.


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The purpose of Ignore mode is that it allows the goal seeking to bequickly turned off and on without having to change data in the GoalSeek & Control Manager (discussed in the next section).

When the goal seeking mode is selected, the Goal Seek and ControlManager option on the View menu is enabled.

Figure 2.2 Select Use from the Goal Seek & Control menu itemon the Analysis menu to instruct AFT Fathom to

perform goal seeking when it runs.

Goal Seek and Control Manager

The Goal Seek and Control Manager is where variables and goals aredefined and applied (Figure 2.3). The Goal Seek and Control Manager isopened by selecting Goal Seek and Control Manager from the ViewMenu.


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There are three tabs on the Goal Seek and Control Manager, and the firsttwo will be used most frequently. These are the Variables tab and theGoals tab. Variables and goals are discussed in then next few sections.

Figure 2.3 Goal Seek and Control Manager is where you defineand apply your variables and goals.

GSC variables

Variables are input parameters that the GSC module will change toachieve the user's desired goals. Variables are defined and applied fromthe Variables tab on the Goal Seek and Control Manager window (see

Figure 2.4). Generally, there must be one variable applied for each goalthat is applied.

Types of variables

All variables are junction parameters. The variables that are available foreach junction type are shown in Table 2.2. There are over 30 types ofvariables.

12 AFT F h 7 0 M d l U G id


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Figure 2.4 GSC Variables are input parameters to be

automatically varied.

Creating and deleting variables

To create a variable, click the New Variable button on the Variables tab(Figure 2.4). This will insert a new item into the variable list. After thevariable has been added, the variable data is defined by entering thenecessary data in each of the data columns.

Variables may also be added by duplicating an existing variable, thenmodifying the data for the new variable. To duplicate a variable, selectthe variable to be duplicated from the variable list, and click the

Duplicate Variable button.To delete a variable, select the variable by clicking on the appropriaterow in the variable list. After selecting the variable to be deleted, clickthe Delete Variable button. If you want to delete all of the variables inthe list, click the Delete All Variables button.


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14 AFT Fathom 7 0 Modules Users Guide


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14 AFT Fathom 7.0 Modules User s Guide

Table 2.2b List of object types with available variables

Object Type Variables Restrictions

Three Way Valve Open Percentage

Valve Loss Value

Elevation Only exit valves

Venturi Loss Factor

Applying variables

Once a variable has been created, the user must specify if a variable is tobe used when the GSC module is run. To apply a variable, select thecheckbox in the Apply column.

Using the Apply feature allows the user to define multiple variables thatcan be used in alternate cases or analyses. Any of the variables that arenot being used for a particular analysis can remain in the list for lateruse. Click the Apply checkbox for the variables that are to be used in thecurrent analysis.

Object type

The Object Type defines whether the variable applies to a pipe or ajunction. At this time, variables may only be assigned to junction objecttypes.

Junction type

The Junction Type column is used to define the type of junction towhich the variable is being applied.

Junction number and name

The specific junction to vary is selected in the Junction Number andName column. The list will only display junctions of the type selected inthe Junction Type column.

Variable parameter

Each junction type has a specific set of parameters that are available asvariables (Table 2.2). The list will only display parameters that are

available for the junction type selected in the Junction Type column.



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Linking variables

The Link To column is used to force a variable on multiple junctions ofthe same type to solve to the same value.

An example where this would be desirable would be when using pumpimpeller trim as a variable for several pumps in parallel. It is oftendesirable to solve for a condition where the pump impeller trim is thesame for all of the pumps. This can be accomplished by using variablelinking. A pump impeller trim variable would be defined for each of thepumps. Then, one of the pumps would be selected as the basis pump,which just means no linking is specified for this pump. The other pumpswould be linked to the basis pump by selecting the basis pump from thelist in the Link To column.

Variable bounds

During a goal search, the GSC module will modify the values for thedefined variables. Sometimes it is helpful to specify upper and lower

bounds for variables to provide logical extremes during the goal search.Some examples of logical bounds that can be applied would be lowerand upper bounds on valve open percentage of 0% and 100%,respectively.

Note that bounds can have engineering units, but these units are notdisplayed. It is assumed the units are the same as the junction inputparameter specifications window.

Reviewing junction input data

If you would like to see the input data for the junction selected as avariable, press the right mouse button on the far left column in theVariables table. The inspection window will display, showing you theinput data.

Editing junction input data

Similar to the inspection feature just described, you can open theJunction Specifications window by double-clicking the far left column inthe Variables table. From there you can change any data desired.



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16 AFT Fathom 7.0 Modules User s Guide

GSC goals

Goals are output values you would like to achieve. The GSC moduleadjusts the applied variables until the applied goals are met. Goals aredefined and applied on the Goals tab on the Goal Seek and ControlManager window (Figure 2.5). Generally there should be one goalapplied for each applied variable.

Figure 2.5 GSC Goals are output parameters to be achieved bychanging the variables.

Types of goals

The GSC module offers over 150 goals applied to pipes, junctions orgroups of pipes and/or junctions. Table 2.3 lists all of the types of goals.



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p g

Table 2.3a List of object types with available goals

Object Type Goals Restrictions/Comments

Pipe Energy Gradeline

Head Gradient

Head Loss

Heat Rate Into Pipe Only with heat transfer

Hydraulic Gradeline

Mass Flow Rate

Pressure Drop Friction

Pressure Gradient

Pressure StagnationPressure Static

Pressure Static Maximum

Pressure Static Minimum

Temperature Only with heat transfer

Temperature Loss Only with heat transfer

Velocity

Volumetric Flow Rate

Wall Temperature Only with heat transferArea Change Energy Gradeline

Bend Hydraulic Gradeline

Check Valve Mass Flow Rate

General Component Pressure Stagnation

Jet Pump Pressure Static

Orifice Temperature Only with heat transfer

Relief Valve Volumetric Flow Rate

Screen

Valve

Venturi

Volume Balance

Assigned Flow Energy Gradeline

Hydraulic Gradeline

Pressure Stagnation

Pressure StaticAssigned Pressure Mass Flow Rate Net Into Jct Net flowrate

Vol. Flow Rate Net Into Jct Net flowrate



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Table 2.3b List of object types with available goals (cont.)


Branch Energy Gradeline

Hydraulic Gradeline

Mass Flow Rate Net flowrate

Pressure Stagnation

Pressure Static


Volumetric Flow Rate Net flowrate

Control Valve Cv If Open Pct data exists

Energy Gradeline Only for FCVHead Loss Not PDCV

Hydraulic Gradeline Only for FCV

Mass Flow Rate Only for PRV, PSV

Open Percentage If Open Pct data exists

Pressure Loss Not PDCV

Pressure Stagnation Only for FCV

Pressure Static Only for FCV


Volumetric Flow Rate Only for PRV, PSV

Dead End Energy Gradeline

Pressure Stagnation

Heat Exchanger Energy Gradeline

Heat Rate In Only with heat transfer. For non-

fixed heat rate exchanger models.

Hydraulic GradelineMass Flow Rate

Pressure Stagnation

Pressure Static

Temperature Only with heat transfer. For non-

controlled temperature models.Volumetric Flow Rate



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Table 2.3c List of object types with available goals (cont.)


Pump Energy Gradeline

Head Rise Only for non-fixed head rise pumps

Hydraulic Gradeline

Mass Flow Rate Only for non-fixed flow pumps

NPSH Margin

Power Overall

Pressure Rise Only for non-fixed head rise pumps

Pressure Stagnation

Pressure StaticTemperature Only with heat transfer

Volumetric Flow Rate Only for non-fixed flow pumps

Reservoir Mass Flow Rate Net Into Jct Net flowrate

Vol. Flow Rate Net Into Jct Net flowrate

Spray Discharge Mass Flow Rate Out Net flowrate

Volumetric Flow Rate Out Net flowrate

Tee or Wye Energy Gradeline

Hydraulic GradelinePressure Stagnation

Pressure Static


Three Way Valve Energy Gradeline

Hydraulic Gradeline

Pressure Stagnation

Pressure StaticTemperature Only with heat transfer

Group Sum Head loss

(pipes and junctions) Heat rate in Only with heat transfer

Mass flow rate

Pressure loss

Volumetric flow rate

Group Max/Min Uses all pipe goals Same as pipe goals

PipesGroup Max/Min Use all junction type goals Same as junction goals

Junctions

Creating and deleting goals

To create a goal, click the New Goal button on the Goals tab. This willinsert a new item into the goals list. After the goal has been added, the



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goal data is defined by entering the necessary data in each of the datacolumns.

Goals may also be added by duplicating an existing goal, then modifyingthe data for the new goal. To duplicate a goal, select the goal to beduplicated from the goal list, and click the Duplicate Goal button.

To delete a goal, select the goal by clicking on the appropriate row in thegoal list. After selecting the goal to be deleted, click the Delete Goalbutton. If you want to delete all of the goals in the list, click the DeleteAll Goals button.

Applying goals

Once a goal has been created, the user must specify if a goal is to beused when GSC is run. To apply a goal, select the checkbox in the Applycolumn.

Using the Apply feature allows the user to define multiple goals that canbe used in alternate cases or analyses. Any of the goals that are not beingused for a particular analysis can remain in the list for later use. Clickthe Apply checkbox for the goals that are to be used in the currentanalysis.

Goal types

Users may specify three types of goals when using the GSC module.

Point Goal A point goal is specified when the desired goal can bespecified at a specific object location in the model.

Differential Goal A differential goal is used when the goal value isactually determined by the difference in values between two specificobject locations. An example of a differential goal might be thepressure difference between two locations in the model.

Group Goal A Group goal is used when a goal is to be applied to agroup of objects at the same time. In order to use a Group goal, all ofthe objects must be added to a Group by using the Groups commandon the Edit menu.


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GSC data in Model Data

When the GSC module is active, the Model Data window displays a list

of all variables and goals in the General section. This is useful fordocumentation purposes. See Figure 2.6.

Figure 2.6 Model Data window shows the variable and goal input

data.

GSC feedback during the solution

Figure 2.1 depicted the logic flow when running AFT Fathom with goalseeking enabled. When a goal seeking model is run, the Solution

Progress window displays additional information (Figure 2.7).As shown in Figure 2.7, at the far right is how many calls have beenmade to the Hydraulic Solver. This relates to the Figure 2.1 iterationloop from the Hydraulic Solver to the Numerical Optimizer, and howmany times GSC has gone around the loop.

The Best (Lowest) field shows the progress towards satisfying the GSCgoals. As progress is made, this field will approach zero. This relates to



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the diamond in Figure 2.1 which checks goal convergence. This occurswhen the Best (Lowest) value is sufficiently small.

GSC informationdisplayed on this line

As progress is made,this should approach

zero

Number of calls to theHydraulic Solver

displayed here

Figure 2.7 The Solution Progress window shows additional

information when a GSC model is run.

GSC data in output

When the GSC module is active and goal seeking is enabled, the Outputwindow displays a GSC Variables tab and GSC Goals tab in the General

section (see Figure 2.8). If the goal seeking was successful, the GSCGoals tab (Figure 2.8 bottom) should show the Actual Goal Value(i.e., the result from the hydraulic solution) close or equal to the UserGoal Value specified in the Goal Seek and Control Manager.

If the Actual Goal Value and User Goal Value differ significantly, theuser is given a warning. This can occur for a variety of reasons, and isdiscussed in detail later in this chapter.



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The GSC Variable tab (Figure 2.8 top) shows the input values that mustexist in order to satisfy the goals.

Figure 2.8 Output window shows the solved variable values andthe users goal and actual solved goal values.

Changing input values to GSC results

As discussed previously, the Output window GSC Variables tab (Figure2.8 top) indicates how the input parameters must be varied to satisfy thegoals. Once you have these results, you may want to keep and use themin the model. There are two ways to do this: Transferring Results toInitial and generating a Disconnected Scenario.

Transferring results to initial

In general, the Output window supports a feature called TransferResults to Initial Guesses. This is available on the Edit menu. Whenused without the GSC module, it transfers calculated results for flow,

pressure and temperature to the initial guess values of the pipes andjunctions. When used after a GSC run it gives you three options: totransfer the GSC Variable Data, the calculated results, or both (seeFigure 2.9).

If you choose either of the first two options that transfer GSC VariableData, the junction data on the Specifications window will be changed tothe GSC Variable results (i.e., Figure 2.8 top). This means that one could


h h l ki h d l d b i h


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then choose to Ignore goal seeking, rerun the model, and obtain the sameresults as before.

Figure 2.9 Transfer Results window opened from the Output

window Edit menu allows users to transfer GSCVariable data back to the input fields

Generating a disconnected scenario

Scenarios and Scenario Manager are discussed in depth in the AFTFathom 7.0 Users Guide. After a run is complete, a special type ofscenario can be created called a disconnected scenario. A disconnectedscenario itself breaks the inheritance of normal child scenarios so that itis a truly standalone scenario. This is ideal for GSC results in that it maynot make sense to save the GSC results for future use if the model canotherwise be changed in arbitrary ways. For if it were changed, the GSCresults would be invalidated, meaning the user would need to rerun GSC.

For example, assume a GSC run is made to find the valve open positionrequired to achieve a certain flow. If this result is saved, and then the

pipe size is later changed, the valve open position would no longersupply the desired flow. The pipe size could be changed, for instance,within the particular scenario or perhaps in an ancestral scenario.

What one may want in such cases is topreserve the GSC results and allinput data that accompanied it. That is the purpose of the disconnectedscenario. Disconnected scenarios cannot be changed by other scenarios,but only in the disconnected scenario itself.


T t di t d i i th O t t i d h


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To create a disconnected scenario, in the Output window chooseGenerate Disconnected Scenario from the View menu or Toolbar.

When goals cannot be achieved

In some cases the GSC module may not be able to achieve a goal. Thiscan happen for the following reasons:

1. A goal is not physically realistic

2. A better starting point is needed for the input values assigned asGSC Variables

3. Hydraulic solution tolerances or optimizer numerical parametersrequire adjustment

In such cases, the goal will not be satisfied in the results. In other words,the Actual Goal Value and User Goal Value will differ (Figure 2.8bottom).

In all cases the user will be warned when goals were not met. Figure2.10 shows the Output window with such a warning.

Figure 2.10 Warning display in Output window when a goalcannot be met.


Physically unrealistic goals


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Physically unrealistic goals

It may be possible that a goal is not achievable because it is notphysically possible. For example, a pump may be too small to satisfy aflowrate goal at some pipe.

To determine whether a goal is unrealistic, try changing the goal andrerunning the model. If the goal can be met in some cases and not others,this is an indicator that the original goal was unrealistic.

Better starting point needed

In some cases the goal may be so far away from the original model thatthe GSC module has difficulty finding a solution. This is not common,but it is worth trying to adjust the starting point of parameters which arebeing varied.

Changing control parameters

The Numerical Optimizer determines goal search directions byapproximating a gradient based on perturbed variable values. By defaultit uses a central difference approximation, but forward difference canalso be used. If the hydraulic solution is not converged to a sufficientlysmall tolerance, the gradient approximation will not be sufficientlyaccurate and hence a good search direction cannot be obtained. The endresult is that the goal seeking fails.

There are two general areas that can be changed in such cases: thehydraulic solution tolerances in Solution Control, and numerical controlparameters in the Goal Seek and Control Manager.

In the next few sections recommendations on how to manually changethese parameters will be given. However, before making a manualchange it is definitely worth trying the automated parameter adjustmentfeature.

Figure 2.10, bottom picture, shows the warning when a goal is not met,and also shows a recommendation and suggests pressing the F2 key.When doing so, a window appears as shown in Figure 2.11. Thiswindow will offer up to three options for automatic parameteradjustment. It is typically a good idea to accept the default changes, clickOK, and rerun the model.


The purpose of the Figure 2 11 window is to simplify for the user


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The purpose of the Figure 2.11 window is to simplify for the usermaking common changes to resolve goal seeking problems.

Figure 2.11 When goal seeking fails, pressing the F2 key will show

this window which allows the user to automaticallyimplement recommend numerical parameteradjustments.

Caution: The user should be very cautious in manually changingparameters in Solution Control and the Goal Seek and Control Managernumerical control. Making changes without a good understanding of the

parameters involved can lead to incorrect results.

Changing tolerance in Solution Control

By default AFT Fathom uses Relative Tolerance criteria set to 0.0001(see Figure 2.12). Goal seeking convergence can sometimes be improvedby reducing these values to 0.00001 or 0.000001.

For a more in-depth discussion of Solution Control see the AFT Fathom7.0 Users Guide, Chapter 8.



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Figure 2.12 Reducing Solution Control tolerance criteria mayresolve goal seeking difficulties.

Changing goal seeking numerical control

Figure 2.13 shows the Numerical Control area of the Goal Seek andControl Manager, discussed earlier in this chapter. The most useful

parameter one can adjust is the Relative Finite Difference Step Size.Using values between 0.01 and 0.001 are recommended. In some casesusing a value as high as 0.1 may be tried.

What to do if the Solver gets stuck

Figure 2.1 depicts the logic of how the Hydraulic Solver and NumericalOptimizer work together. Discussed earlier is the issue of physicallyunrealistic goals. Occasionally the user may have specified a goal whichis in fact physically realistic, but in the process of going from aphysically realistic starting point to a similarly physically realistic goal,a physically unrealistic system may be proposed by the NumericalOptimizer. What happens in such cases?



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Adjusting finitedifference step

size can resolvedifficulties

Figure 2.13 Changing certain numerical control parameters in the

Goal Seek and Control Manager may resolve goalseeking difficulties.

When performing goal seeking with the GSC module, AFT Fathom hasbeen designed to gracefully handle such cases. One of two things will

typically happen:

1. The Hydraulic Solver will experience a computational error

2. The Hydraulic Solver will not be able to converge

In the first case, AFT Fathom does not stop and tell the user of the error,but instead sets an internal flag that the system used for the particulariteration that caused the error was a poor system and should not be

considered further by the Numerical Optimizer. In other words, it skipsthe system that caused the error. This will happen in a way which istransparent to the user and requires no intervention.

The second case is of more interest here. In this case the HydraulicSolver gets stuck on one of the systems proposed by the NumericalOptimizer and cannot progress. The Hydraulic Solver will continuetrying to converge until it reaches the iteration limit. Once it reaches that


limit, it will react in a similar way to the first case above it will set a


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yflag and skip that system.

However, the default maximum number of iterations is 50,000 (specified

in Solution Control, Figure 2.14). It is perfectly fine for one to wait untilthis limit is reached and allow the AFT Fathom to handle the situationautomatically, but depending on the size of the model it may take awhileto get to 50,000 iterations. In such cases it may be desirable to allowAFT Fathom to more quickly conclude the model will not converge byreducing the maximum iterations to something like 5,000.

Tip: If the Hydraulic Solver appears to get stuck while performing aGSC run, you can pause the Solver, open the Solution Control window,and reduce the Maximum Iterations. The default value is 50,000.Depending on the model size, a reduced value of 5,000 may beappropriate.

Figure 2.14 It may be desirable to reduce the Solution ControlMaximum Iterations when performing goal seeking.


GSC data differences across scenarios


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GSC variables and goals will appear in all scenarios. In other words, you

cannot create a variable or goal that will appear in some scenarios andnot others. However, the application of variables and goals can differfrom scenario to scenario. This allows you to perform goal seeking withdifferent variables and goals across scenarios.

Variable and goal

application can differbetween scenarios

Figure 2.15 Goal Seek and Control Manager allows one to applyand unapply variables and goals. The application of

goals and variables can be modified betweenscenarios.

C H A P T E R 3


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C H A P T E R 3

Goal Seek and Control Example

This example demonstrates the fundamental concepts of the Goal Seekand Control (GSC) add-on module by way of example. The exampleshows how GSC can be used to size pumps as part of a system designprocess.

A number of other GSC example model discussions are included in aHelp file distributed with AFT Fathom called FathomExamples.hlp. Itcan be opened from the Help menu by choosing Show Examples.

Note: This example can only be run if you have a license for the GSCmodule.

Topics covered

Using Goal Seek and Control Manager

Defining GSC Variables and Goals

Using pump head rise as a GSC Variable

Using Group Max/Min goals

Required knowledge

This example assumes that the user has some familiarity with AFTFathom such as placing junctions, connecting pipes, entering pipe and


junction specifications, global editing, and creating groups. Refer to theAFT F th U ' G id f i f ti th t i


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AFT Fathom User's Guide for more information on these topics.

Model file

This example uses the following file, which is installed in the Examplesfolder as part of the AFT Fathom installation:

Pump Sizing and Selection with FCV.fth (GSC Example Scenario)AFT Fathom model file

This example is provided in the model file under the SI Units scenario. Itis also provided in English units under the English Units scenario.

Problem statement

The piping for a heat exchanger system is being designed. The system

will pump supply water from a tank pressurized to 70 kPa(g) with aliquid surface elevation of 2 meters to a receiving tank with a pressure of200 kPa(g) and a liquid surface elevation of 3 meters. The heatexchangers operate in parallel. The flow through the heat exchangers iscontrolled to 25 m3/hr by two flow control valves. There is a designrequirement that the control valves have a minimum pressure drop of 35kPa.

Use GSC to size the pump.

Step 1. Start AFT Fathom

From the Start menu, choose AFT Products and AFT Fathom.

Step 2. Specify system properties

1. Open the System Properties window by selecting System Propertiesin the Analysis menu

2. On the Fluid Data Tab, select the AFT Standard database and thenselect water at 1 atm in the fluids available window

Chapter 3 Goal Seek and Control Example 35

3. Click Add to Model to select water for use in this model


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4. Type in 21 C in the fluid temperature box

5. Click Calculate Properties6. Select OK

Step 3. Build the model

A. Place the pipes and junctionsAt this point, the first four items are completed on the Checklist. Thenext Checklist item is to Define Pipes and Junctions. In the Workspacewindow, assemble the model as shown in Figure 3.1.

Figure 3.1 Layout of pipe system for Pump Selection with FlowControl Valves Example


B. Enter the pipe data


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The system is in place, but now you need to enter the input data for thepipes and junctions. Double-click each pipe and enter the following data

in the Specifications window (or use the Global Pipe Editing window):

All of the pipes are Steel, with standard roughness and the followingdata:

Pipe Length

(meters)

Size Type

P1 6 2 inch (5.3 cm ID) Schedule 40





P6 6 2 inch (5.3 cm ID) Schedule 40P7 20 2 inch (5.3 cm ID) Schedule 40



C. Enter the junction data

J1 Reservoir

1. Name = Supply Tank

2. Tank Model = Infinite Reservoir (only visible if XTS module isenabled)

3. Liquid Surface Elevation = 2 meters4. Surface pressure = 70 kPa(g)

5. Pipe Depth (on Pipe Depth and Loss Coefficients tab) = 2 meters

J9 Reservoir

1. Name = Receiving Tank


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Step 5. Add a variable


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In the GSC module, variables are the parameters that AFT Fathom will

modify in order to achieve the specified goals. In general there should beone applied variable for each applied goal.

Select the Variables tab on the Goal Seek and Control Manager window.The Variables tab allows users to create and modify the systemvariables. The object and junction type are selected, then the name andnumber of the object to which the variable applies, and the objectparameter that is to be varied are specified on the Variables tab.

For this example, you will be adding a variable for the Pump Fixed HeadRise. Select the Add Variable button, and input the following variabledata:

1. Apply: Selected

2. Object Type: Junction

3. Junction Type: Pump4. Junction Number and Name: J2 (Pump)

5. Variable Parameter: Head Rise

6. Link To: (None)

7. Lower Bound: Leave Blank

8. Upper Bound: Leave BlankThe Apply column allows users to specify which of the variables thathave been defined will be used. This allows the flexibility of creatingmultiple variable cases, while only applying selected variables for anygiven run.

The Link To column allows users to apply the same variable to multipleobjects. This allows users to force parameters for several objects to be

varied identically.

Upper and lower bounds provide logical extremes during the goalsearch. For this case, leave the lower and the upper bounds blank.

After entering the data, the Variable tab should appear as shown inFigure 3.3.


Step 6. Add a goal


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Goals are the parameters you want to achieve. The goals are achieved as

AFT Fathom modifies the variables. Typically, there should be oneapplied goal for each applied variable.

Figure 3.3 GSC Variables are parameters that are changed by

AFT Fathom to achieve the defined goals.

Select the Goals tab on the Goal Seek and Control Manager window.The Goals tab allows users to create and modify the system goals. Thegoal type, object type, and the goal parameter are selected. A criterionfor determining if the goal has been met is then specified, along with avalue and units for the goal parameter. The user then selects the object to

which the goal applies, and, if applicable, the location on the object atwhich the goal applies (e.g., the inlet or outlet of a pipe object).

The Apply column allows users to specify which of the goals that havebeen defined will be used. This allows the flexibility of creating multiplegoal cases, while only applying selected goals for any given run.

A Group Max/Min goal allows a single goal to be applied to a group of

objects. Fathom applies a Group Max/Min goal by ensuring the final


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Figure 3.4 GSC Goals are the parameter values the user wants to

achieve.

As variables and goals are added to a model, AFT Fathom will displaysymbols beside the pipes and junctions that have variables or goalsapplied to them. The default is a V for variables, and a G for goals.

The goal symbol is not displayed next to objects that are part of a groupgoal. This is illustrated in Figure 3.5. These symbols can be configuredon the Workspace Preferences window.



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V symbol for aGSC Variable.

G symbols forGSC Goals are

not displayed forGroup goals.

Figure 3.5 AFT Fathom displays symbols next to objects on theWorkspace that have goals or variables defined.

Step 7. View GSC settings in Model Data

The Model Data window provides a summary of the GSC modulevariable and goal definitions. Once the variable and goal information hasbeen added in the Goal Seek and Control Manager, the information isdisplayed on the Goal Seek and Control tab in the General section of the

Model Data Window. Figure 3.6 shows the GSC variable and goalinformation as it was entered for this example.



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Figure 3.6 The Goal Seek and Control parameters defined in theGoal Seek and Control Manager are displayed in the

General section of the Model Data window.

Step 8. Enable goal seeking

After the GSC goals and variables have been defined, goal seeking mustbe enabled using the Analysis menu, as shown in Figure 3.7.

Step 9. Run the model

Select Run Model in the Analysis menu. This will open the SolutionProgress window. This window allows you to watch as the AFT FathomSolver converges on the answer.

Note:When using the GSC module there is an area displayed inSolution Progress that shows the specific progress of the GSC module.As it makes progress, the Best (Lowest) value will decrease towardszero. The field in the far right displays how many complete hydraulicsolutions have been run.

After completion, click the View Output button at the bottom of theSolution Progress window.



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Figure 3.7 Select Use from the Goal Seek & Control menu itemon the Analysis menu to instruct AFT Fathom to dogoal seeking when it runs.

Step 10. Examine the results

The Output window contains all the data that was specified in the OutputControl window. The results of the GSC analysis are shown in theGeneral Output section.

The GSC Variables tab shows the final values for the variable

parameters, as shown in Figure 3.8. The GSC Goals tab shows the valuesachieved for the goals, as shown in Figure 3.9.



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Figure 3.8 The final GSC Variable values are shown on the GSCVariables tab in the Output window General section.

Figure 3.9 The final GSC Goal values are shown on the GSC Goalstab in the Output window General section. The Actualand User values should be close if GSC was successful.If not, a warning will appear.

Analysis summary

For this example, the minimum goal of 35 kPa pressure drop across theflow control valves was achieved by applying a Group Max/Min goal.The pump head requirement for the example system was determined tobe 54.9 meters, as shown in Figure 3.8.

The pump head requirements for this system could also be determinedwithout GSC by adjusting the pump head rise, and running multipleFathom solutions until the minimum control valve pressure droprequirement was met. Alternatively, one could change the pump to afixed flow pump, and allow Fathom to calculate the pump headrequirement directly. However, this technique results in a referencepressure problem between the assigned flow pumps, and the flow control

valves. To bypass this problem, one of the flow control valves must bechanged to a constant pressure drop valve with a 35 kPa pressure drop,until a pump head could be determined.

By using the GSC module to size the pump, the head requirements canbe determined directly without user iterations or modifications to theflow control valves.

C H A P T E R 4


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Modeling Extended Time Simulation

This chapter discusses how one uses the XTS module to model transientsystem behavior. Detailed information regarding XTS menus andfunctionality is given in this chapter. Chapter 6 provides a detailedhands-on XTS example.

What is the XTS module?

While steady-state modeling answers many design questions, somequestions cannot be adequately answered without considering howsystems behave over time. Questions such as how long it will take to filla tank require a dynamic system model. The AFT Fathom XTS moduleanswers such questions.

The XTS module allows you to model transient system behavior. Userscan specify the time duration of the simulation, time step size, controlsystem parameters, and how components such as pumps and valvesoperate over time. Operations such as valve position changes can occurduring a specified time schedule, or can occur in response to events in

the system thereby simulating control system actions.Users can also specify tank volume on finite tanks, so that tankdraining and filling can be simulated. Tanks can be open or pressurized,with the gas pressure automatically calculated as the liquid levelchanges.

The XTS module is a powerful tool which extends AFT Fathomspowerful modeling capabilities into the dimension of time.


How does the XTS module work?

The XTS module can be described as using a lumped or quasi-steady


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g p q y

approximation to time simulation. What it in fact does is represent thetransient system behavior as a sequence of pseudo-steady-state solutions.In between each pseudo-steady-state solution it adjusts transientparameters, performs mass balances on tanks, and changes componentoperations as specified by the user.

As a thought experiment, consider a system which you want to simulatefor ten minutes in one minute increments. This would require eleven

time step solutions (time zero and each minute up to ten). You couldmanually do this with standard AFT Fathom by running a steady-statemodel eleven times, and in between each run adjusting the inputparameters for the next run based on the results of the previous run. TheXTS module automates this manual process.

Besides the automation benefits, the XTS module offers additionalbenefits such as transient output data management, consolidation and

display, and graphing tools to review the transient results.

Using the XTS module

The user has the option of activating or not activating the XTS modulewhen AFT Fathom first loads. After AFT Fathom is loaded, the XTS

module can be activated or deactivated for use from the Options menu.Whether or not XTS is activated impacts the Analysis menu, Checklistand Status Bar and multiple other AFT Fathom functions.

If the XTS module is active, the user can still run models in Steady Onlymode by selecting this under Time Simulation on the Analysis menu.Hence there are three possibilities for XTS.

1. XTS is not active

2. XTS is active and operated in Steady Only mode

3. XTS is active and operated in Transient mode

Table 4.1 lists the three possibilities and the impact on various AFTFathom features.

Chapter 4 Modeling Extended Time Simulation 49

Table 4.1 AFT Fathom feature accessibility based on XTSactivation and Time Simulation mode

XTS Not Active XTS Active XTS Active


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Feature No Mode Steady Only Mode Transient Mode

"Time Simulation" on Analysis

MenuNot Visible Visible Visible

"Transient Control" on

Analysis MenuNot Visible Visible but disabled Visible and enabled

"Transient Control" on

ChecklistNot Visible Visible but disabled Visible and enabled

"Transient Control" on Status

BarNot Visible Not Visible Visible

"Transient" tab on Junction

Specifications Windows

Not Visible - data

cannot be entered

Visible - data can be

entered but will not be

used

Visible - data can be

entered and will be

used

Transient Pipe and Jct tabs in

Output ControlNot Visible Visible Visible

"Transient" tab in Junction

Section of Model DataNot Visible

Visible only if junction

transient data exists

Visible only if junction

transient data exists

Time control slider and

buttons in Output windowNot Visible Not Visible Visible

Time control slider and

buttons in Visual ReportNot Visible Not Visible Visible

"Transient" tabs on Output

WindowNot Visible Not Visible Visible

"Transient" tab on Select

Graph DataNot Visible Not Visible Visible

Animation controls on Graph

ResultsNot Visible Not Visible Visible when selected

Enabling XTS transient mode

When the XTS module is active, two new menu items appear on theAnalysis menu. At the top of the Analysis menu is the Time Simulationmenu, from which the user can select Steady Only or Transient.


The XTS Transient analysis mode is enabled by selecting TimeSimulation -> Transient from the Analysis menu (Figure 4.1). This canbe selected before or after a model is built. Pre-existing models built

ith t d d AFT F th b d ith XTS d t i t d

Documents

Fathom 7.0 Modules Guide SI