ChENGINEER SPACE

This is a short instruc­tion to how to install EMSO on last Ubuntu ver­sion: 10.04 LTS (code­name Lucid Lynx). First of all get the last releases of EMSO and VRTherm here. VRTherm is a ther­mo­dy­namic prop­er­ties pack­age that works as a plu­gin of EMSO. Cur­rently the last ones are emso-beta-linux2-i386-0.10.3.tar.gz and vrtherm-linux2-i386-1.4.2.tar.gz. So that untar them:

If you want to have EMSO and VRTherm avail­able for all users you should copy them to a com­mon place:

And cre­ate sym­bolic links to call EMSO and VRTherm:

So you can call them any­where by typ­ing in the terminal:

Let’s start get­ting all the pack­ages nec­es­sary from Ubuntu repository.

And finally the libfox1.4 pack­age must be tak­ing from an old repos­i­tory. It is essen­tial to run EMSO and VRTherm promptly:

Addi­tion­ally to run all sam­ples you should give write per­mis­sion to folder /mso/sample (or copy it to your /home folder). EMSO needs to cre­ate tem­po­rary files to open dia­gram files (.PFD) oth­er­wise EMSO crashes.

To start using EMSO for all appli­ca­tions you must prop­erly con­fig­ure the ther­mo­dy­namic pack­age. Call EMSO and go to “Con­fig” > “Plu­g­ins…” and add a plu­gin calls PP and the path to the file libvrpp.so under /usr/local/vrtherm/libvrpp.so as shown in Fig­ure. Press­ing “Add Plu­gin” and “Ok”, PP will be shown in “Reg­is­tered Plu­g­ins” sec­tion above. EMSO will be ready after restart application.

This post starts to our sec­tion of HOW-TO texts. My obje­tive with this spe­cific post is to intro­duce using some free tools to dif­fer­ent applications.

A clas­sic prob­lem in process engi­neer­ing is the case of a dynamic tank where the out­put flow is pro­por­tional to its level (Fig. 1). This exam­ple is part of EMSO tuto­r­ial so that more details would be to con­sult in the EMSO man­ual.

Fig. 1. Dynamic tank.

In this approach­ing, the prob­lem of dynamic tank involves 3 vari­ables and 2 para­me­ters such below:

Vari­ables:

• Fⁱⁿ: Input flow (m³/h)
• F^out: Out­put flow (m³/h)
• h: Tank level (m)

Para­me­ters:

• A: Tank area (m²)
• k: Valve con­stant (m^2.5/h)

This sys­tem is mod­eled as sim­ple mate­r­ial bal­ance given to:

where the pro­pri­eties are con­sid­ered con­stants so that, the vol­ume that goes into tank minus the vol­ume that goes out tank are equal to accu­mu­lated volume.

The out­put flow is given to valve equation:

where F^out is pro­por­tional to square root of the tank level h and a valve con­stant k.

EMSO mod­el­ing lan­guage is based on con­cepts of object-oriented pro­gram­ing. These kinds of appli­ca­tions get us pos­si­ble to rep­re­sent the prob­lem through a code. As a result, when we are read­ing the code we are also read­ing a descrip­tion of the prob­lem. EMSO mod­el­ing lan­guage presents 3 basic enti­ties: Model, DEVICES, and Flow­Sheet. An flow­sheet of process is rep­re­sented by the entity Flow­Sheet which is con­sti­tuted by a set of com­po­nents calls DEVICES. The DEVICES are equiv­a­lent to the true units of a process. In its turn, the math­e­mat­i­cal descrip­tion of each DEVICES is rep­re­sented by the entity Model.

The Model of a sin­gle tank is given below:

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using "types";
 
Model tank
    PARAMETERS
    k as Real (Brief="Valve constant", Default=4, Unit='m^2.5/h');
    A as area (Brief="Tank area", Default=2);
 
    VARIABLES
in  Fin  as flow_vol(Brief="Input flow");
out Fout as flow_vol(Brief="Output flow");
    h    as length(Brief="Tank level");
 
    EQUATIONS
    "Material balance"
    diff(A*h) = Fin - Fout;
 
    "Valve equation"
    Fout = k*sqrt(h);
end

The line 1 indi­cates that Model used a exter­nal file (“types”) where con­tains all use­ful def­i­n­i­tion of unit of mea­sure­ments such as area (line 6), flow_vol (lines 9–10), length (line 11), etc. In the line 4, the para­me­ters are declared. In the line 8, the vari­ables are declared. The in and out indi­cate that are input and out­put vari­ables respectively.

Since there is a struc­ture that rep­re­sents a sin­gle tank, we can eas­ily model a set of tanks in series (Fig. 2).

Fig. 2. Dynamic tanks in series.

That set of tanks in series can be rep­re­sented by Flow­Sheet below. This struc­ture requires 1 input spec­i­fi­ca­tion (line 32) and 2 ini­tial con­di­tions (line 35). The time of inte­gra­tion, step, and other spec­i­fi­ca­tions to solver are made in the sec­tion OPTIONS (line 39).

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FlowSheet tanks
    VARIABLES
    Fin        as flow_vol;
 
    DEVICES
    tank1      as tank;
    tank2      as tank;
 
    CONNECTIONS
    Fin        to tank1.Fin;
    tank2.Fout to tank2.Fin;
 
    SPECIFY
    Fin = 10*'m^3/h';
 
    INITIAL
    tank1.h = 1*'m';
    tank2.h = 1*'m';
 
    OPTIONS
    TimeStep = 0.1;
    TimeEnd = 2;
    TimeUnit = 'h';
end

The solu­tion of prob­lem can be viewed in the own simulator’s GUI. Plots of vari­ables to an ana­lyze of the sys­tem dynam­ics are showed at Fig. 3–4.

Fig. 3. Tank input and out­put flows.

Fig. 4. Tank levels.