gproms

© Process Systems Enterprise Ltd, 2010

© 2010 Process Systems Enterprise Limited

An introduction to gPROMSgPROMS training course

London27-29 September 2010


Building your own models in gPROMS I. Lumped models



Building your own models in gPROMSI. Lumped models

1. The gPROMS ModelBuilder environment

2. Motivation: why build your own models?

3. First-principles mathematical modelling in gPROMS

4. Degrees of freedom and initial conditions

5. Running a simulation and viewing the results

6. Using the modelling support tools

7. Using arrays and intrinsic functions

8. Modelling systems with discontinuities

9. Constructing composite models

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1. The gPROMS ModelBuilder environment



The working environment of gPROMS

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Project tree area

Entity editor

Menus & toolbars

Topology/flowsheeting

Model Public Interface


Project tree area

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Library Projects (green colour) contain potentially re-usable components (usually) read-only projects Can be referred to by other libraries/projects Example: Process Model Libraries (PML)

Projects (yellow colour) developed by the user consist of several folders/groups each group contains entities used to construct

model-based applications

Cases (blue colour) created once an activity is executed read-only contain all input information and results a complete record of a model-based activity



Alternative representation: model palette

7More suitable in flowsheeting projects


Entity editor formats

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Text

Dialogs

TopologyFlowsheeting



2. Motivation: why build your own models ?

Building your own models in gPROMS - I. Lumped models


Why build your own models ?

1. New applications need to develop first-principle models from scratch

2. Library models are not suitable for each and every application need to customise them

Keep in mind: combination with other models need to comply to some standard: model libraries

gPROMS: an advanced and flexible environment for custom model development

custom model use mix & match with library models

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3. First-principles mathematical modelling in gPROMS



An elementary MODEL: Buffer tank with gravity-driven outflow

outin

dMF F

dt

Equations

mass balance:

calculation of liquid level in the tank:

characterisation of the output flowrate:

Parameters: , A ,

Variables: M, Fin, Fout, h 12

M Ah

out

F h

h

Fout

M

Fin



PARAMETERarea , density AS REALoutlet_flowrate_coefficient AS REAL

VARIABLEinlet_mass_flowrate AS mass_flowrateoutlet_mass_flowrate AS mass_flowratemass_holdup AS massheight AS length

EQUATION

# Mass balance$mass_holdup = inlet_mass_flowrate - outlet_mass_flowrate ;

# Relation of liquid level to mass holdupmass_holdup = density * area * height ;

# Relation of outlet mass flowrate to liquid leveloutlet_mass_flowrate = outlet_flowrate_coefficient * SQRT ( height ) ;


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Parameters

PARAMETERs must be given fixed values before a simulation begins

Supported types: REAL | INTEGER

... | LOGICAL | FOREIGN_OBJECT | ORDERED_SET

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gPROMS language – case convention

gPROMS language is case-insensitive

but...

Convention used by PSE:

all gPROMS keywords in CAPITALS

user-defined identifiers in MixedCase or by separating words with an underscore“_” E.g. ExternalHeatInput or external_heat_input

Use descriptive names!15




EQUATION





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Variables

VARIABLEs may vary with time

Can be either specified by user or calculated by the simulation

VARIABLEs are associated with a VARIABLE TYPE17


Numerical definition:

Default value is used as initial guess for the initialisation calculation.

Lower and Upper bounds define the valid ranges for all Variables of this type: a Variable can never take a value outside this range

Units are not used in the calculation but are very important for model readability and maintainability

A set of commonly used Variable Types is defined in the PML Basics library

based on SI units

look there first before defining your own!

Variable types - II

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EQUATION





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outin

dMF F

dt

M Ah

out

F h

h

Fout

M

Fin


Equations

EQUATIONs can be partial, differential and algebraic

Time derivatives: $HoldUp

Use CTRL+space while typing to obtain list of valid completions

Comments

single line comments:# …

multiple line comments:{…}

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Elementary MODELs – III

Arithmetic operators:

+ - / ^

Built-in functions:SQRT(Height)

Declarative language

order of equations not important !

form of equations (usually) not important !

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4. Degrees-of-freedom and initial conditions




Defining a simulation degrees of freedom - I

Number of variables: 4

Number of equations: 3

need 1 (=4-3) extra specification ("input"), e.g.:

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, , , outin

M F F h

outin

out

dMF F

dt

M Ah

F h

20inF


Defining a simulation degrees of freedom - II

Number of variables: 4

Number of equations: 3

or more generally...

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, , , outin

M F F h

outin

out

dMF F

dt

M Ah

F h

( )in in

F F t



Defining a simulation degrees of freedom - III

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Fin(t)

t

h(t)?

Fout(t)?M(t)?


Defining a simulation initial conditions

At t = 0, we need to determine:

(N.B. Fin(0) already known from upstream unit)

Must satisfy equations at t = 0:

Need one extra equation at t = 0 (“initial condition"), e.g.:

(0) 2.1h

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(0) , (0) , (0) , (0) , (0)outin

M M h F F

(0) (0) (0)

(0) (0)

(0) (0)

outin

out

M F F

M Ah

F h



Defining a simulation initial conditions

Initial conditions can be general equations:

Commonly used initial condition:

Usually …

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(0) 3.2h

i.e. system initially at steady-state

(0)0

dM

dt

Number of Number ofInitial Conditions Differential Variables

=


MODEL vs. PROCESS entities: generic vs specific

A typical MODEL...

Describes physical behaviour in equations, parameters, and variables

Is generic for all unit operations of that type

A typical PROCESS...

Contains all case-specific information needed for simulation Input specifications

Operating procedure

Solver settings (optional)

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Defining a simulation – I

Create a new PROCESS: SimulateTank

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Defining a simulation – II

What MODEL(s) to simulate?

UNIT

T101 AS BufferTank

Simultaneous simulation with multiple instances of the same model :UNIT

T101 AS BufferTank

T102 AS BufferTank

T103 AS BufferTank

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T101

T101 T102 T103



Defining a simulation – III

SET values of PARAMETERs:

SET # Parameter values

T101.area := 1 ; # m2

T101.outlet_flowrate_coefficient := 10 ;

T101.density := 1000 ; # kg/m3

Always need to refer to which model instance (e.g. T101)

Use WITHIN for more compact notation:

SET # Parameter values

WITHIN T101 DO

area := 1 ; # m2

outlet_flowrate_coefficient := 10 ;

density := 1000 ; # kg/m3

END # WITHIN T101

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Assignment symbol in

gPROMS


Defining a simulation – IV

ASSIGN degrees of freedom:

ASSIGN # Degrees of freedom

T101.inlet_mass_flowrate := 20 ;

Or

ASSIGN # Degrees of freedom

T101.inlet_mass_flowrate

:= 20 + 10.0 * SIN ( 22 * 3.14 * TIME / 100 ) ;

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Defining a simulation – V

Initial conditions

INITIAL # Initial conditions

T101.Height = 2.1 ;

If initially at steady-state, specify:

INITIAL

T101.$mass_holdUp = 0 ;

Or:

INITIAL

STEADY_STATE

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INITIAL conditions are equations,

not assignments


Defining a simulation – VI

Specify the SCHEDULE of the operation procedure to be simulated:

SCHEDULE # Operating procedure

CONTINUE FOR 1800

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A complete PROCESS

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UNIT # Equipment itemsT101 AS Buffer_tank

SET # Parameter valuesWITHIN T101 DO

area := 1 ; # m2outlet_flowrate_coefficient := 10 ;density := 1000 ; # kg/m3

END # WITHIN T101

ASSIGN # Degrees of freedomT101.inlet_mass_flowrate := 20 ; # kg/s

INITIAL # Initial conditionsT101.height = 2.1 ; # m

SCHEDULE # Operating procedureCONTINUE FOR 1800


5. Running a simulation and viewing the results




Executing a simulation in gPROMS

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Select the appropriate PROCESS entity

Press the “Simulate…” button to start the simulation (or press F5)

History of already performed simulations


The execution control dialog

Execution specifications

Configuration of Case content

Miscellaneous execution controls

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A Case project is automatically created at the start of the execution



Executing…

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The gPROMS Results Management System (gRMS) is loaded (if selected)

Case project is created

A licence is reserved for the particular Case

Execution output

Stop execution button


Interacting with the execution output:the diagnostics console

Reserve the licence after execution

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The diagnostics console allows you to

query variables, equations, blocks,

units and create model reports and saved

variable sets



Case project structure

Original entities: contain full description of the problem Used to create a new project Easily reproduce results

Trajectories: simulation results Tables, graphs, stream tables, model reports

Problem description: complete definition of the activity in the gPROMS language Used for debugging in relation to the execution output

Execution output: displays all the messages relating to the solution of the Model-based activity

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Viewing the results

View results in Case

time variation of individual variables

stream tables

model reports

gRMS: more powerful environment for configuring graphs

Other output channels

Microsoft Excel®

gPLOT

your own output channels

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Viewing variable results in Case projects

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Viewing results in gRMS

Results are organised in Processes

receive data from gPROMS during activity execution

Management tools: open, save...

Provides facilities for creating 2D & 3D plots

formatting tools and templates

management tools

print, save, export

viewing and exporting data sets

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Constructing a plot in gRMS

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Choose 2D, 3D, XY plot or plot

Template

Click Add line...

Choose a

variable

View/change

line properties


Hands-on session: Simulation of isothermal buffer tankBuilding your own models in gPROMS - I. Lumped models

gproms

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