MATLAB: Error: Complex values are not supported

aspencomplexgamultiobjoptimization

Hi. I'm trying to perform a multiobjective optimization together with aspen plus. I'm using the optimization toolbox (gamultiobj). But after hours, I found the following error: "Complex values are not supported". How should I proceed?

function [TAC] = Objective(x)  
global Aspen 
 
Aspen = actxserver('Apwn.Document.36.0'); 
    [~,mess]=fileattrib; 
    Aspen.invoke('InitFromArchive2',[mess.Name '\SimulationACRYL2.bkp']);
    Aspen.Visible = 1;
    Aspen.SuppressDialogs = 1;
    Aspen.Engine.Run2(1);
    while Aspen.Engine.IsRunning == 1
        pause(0.5);
    end
    
Stages = round(x(1) + 2);
Pressure = x(2);
Feed_Stage = round((Stages-2)*x(3) + 1);
Aspen.Tree.FindNode("\Data\Blocks\B2\Input\NSTAGE").Value = Stages;
Aspen.Tree.FindNode("\Data\Blocks\B2\Subobjects\Column Internals\INT-1\Input\CA_STAGE2\INT-1\CS-1").Value = Stages - 1;
Aspen.Tree.FindNode("\Data\Blocks\B2\Input\PRES1").Value = Pressure;
Aspen.Tree.FindNode("\Data\Blocks\B2\Input\FEED_STAGE\S50").Value = Feed_Stage;
    Aspen.Reinit; % Reinit simulation
    Aspen.Engine.Run2(1); %Run the simulation. (1) ---> Matlab isnt busy; (0) Matlab is Busy;
    time = 1;
    Error = 0;
    while Aspen.Engine.IsRunning == 1 % 1 --> If Aspen is running; 0 ---> If Aspen stop.
        pause(0.5);
        time = time+1;
        if time==40 % Control of simulation time.
            Aspen.Engine.Stop;
            Error = 1;
        end
    end
         
    
Conv = Aspen.Tree.FindNode("\Data\Results Summary\Run-Status\Output\PER_ERROR").Value; 
    if Error == 0 && Conv == 1
       % column cost
        Lang_F = 4.74;
        Diameter = Aspen.Tree.FindNode("\Data\Blocks\B2\Subobjects\Column Internals\INT-1\Input\CA_DIAM\INT-1\CS-1").Value;
        Number_trays = double(Aspen.Tree.FindNode("\Data\Blocks\B2\Input\NSTAGE").Value - 2);
        height_Column = 0.5*(Number_trays)+2;
        heat_reboiler = (Aspen.Tree.FindNode("\Data\Blocks\B2\Output\REB_DUTY").Value)*4.1868;
        Presure_project = 441.3;
        Tension = 108000;
        Column_thickness = ((Presure_project*Diameter)/((2*Tension*0.85)-(1.2*Presure_project))) + 0.003;
        Density_carbon_steel = 7861.1;
        Column_side_volume = 3.14*Column_thickness*height_Column*Diameter;
        Column_side_mass = (Column_side_volume*Density_carbon_steel)*2.205;
        External_radius = (Diameter + 2*Column_thickness)/2;
        Cover_volume = 4*3.14*(External_radius^2)*Column_thickness*2;
        Cover_mass = (Cover_volume*Density_carbon_steel)*2.205;
        total_mass =  Column_side_mass + Cover_mass;
        Cv = exp((7.2756 + 0.18255*(log(total_mass))) + (0.02297*((log(total_mass))^2)));
        Diameterft = Diameter*3.281;
        height_Columnft = height_Column*3.281;
        Cpl = 300.9*((Diameterft)^0.63316)*(height_Columnft^0.80161);
        Factor_material_column = 1;
        FNT = 1;
        FTT = 1;
        FTM = 1; 
        CBT = 468*exp(0.1739*Diameterft);
        CT = CBT*FTM*FTT*FNT*Number_trays;
        CP = Factor_material_column*Cv + Cpl;
        Cost_column = CP + CT;
        
        % condenser cost
        Temp_out_fluid_cold = 20;
        Temp_in_fluid_cold = 5;
        Temp_in_fluid_hot = Aspen.Tree.FindNode("\Data\Streams\S4\Output\TEMP_OUT\MIXED").Value; 
        Temp_out_fluid_hot = Aspen.Tree.FindNode("\Data\Streams\S4\Output\TEMP_OUT\MIXED").Value;
        Temperature_exchange_termic = ((Temp_in_fluid_hot - Temp_out_fluid_cold) - (Temp_out_fluid_hot - Temp_in_fluid_cold))/log((Temp_in_fluid_hot - Temp_out_fluid_cold)/(Temp_out_fluid_hot - Temp_in_fluid_cold)); 
        Factor_exchange_termic = 0.85;
        coefficient_exchange_termic = 850;
        Heat_condenser = (Aspen.Tree.FindNode("\Data\Blocks\B2\Output\COND_DUTY").Value)*4.1868;
        Area_condenser = ((Heat_condenser)/(Temperature_exchange_termic*coefficient_exchange_termic*Factor_exchange_termic))*10.76;
        Cost_condenser = exp(11.0545 - 0.9228*(log(Area_condenser)) + 0.09861*(log(Area_condenser)^2)); 
        Pipe_length = 1;
        Type_Material_Condenser = 1;
        pressure_condenser = 1;
        Condenser_total_cost = Cost_condenser*Pipe_length*Type_Material_Condenser*pressure_condenser;
        
        %Reboiler cost
        Temp_in_fluid_hot_reboiler = 127.5;
        Temp_out_fluid_hot_reboiler = 127.5;    
        Temp_out_fluid_cold_reboiler = Aspen.Tree.FindNode("\Data\Streams\12\Output\TEMP_OUT\MIXED").Value;
        Temp_in_fluid_cold_reboiler = Aspen.Tree.FindNode("\Data\Streams\12\Output\TEMP_OUT\MIXED").Value;
        Temperature_exchange_termic_reboiler = ((Temp_in_fluid_hot_reboiler - Temp_out_fluid_cold_reboiler) - (Temp_out_fluid_hot_reboiler - Temp_in_fluid_cold_reboiler))/log((Temp_in_fluid_hot_reboiler - Temp_out_fluid_cold_reboiler)/(Temp_out_fluid_hot_reboiler - Temp_in_fluid_cold_reboiler)); 
        Factor_exchange_termic_reboiler = 0.85;
        coefficient_exchange_termic_reboiler = 1560;
        Area_reboiler = ((heat_reboiler)/(Temperature_exchange_termic_reboiler*coefficient_exchange_termic_reboiler*Factor_exchange_termic_reboiler))*10.76;
        Cost_reboiler = exp(11.967 - 0.8709*(log(Area_reboiler)) + 0.09005*(log(Area_reboiler)^2)); 
        Pipe_length_reboiler = 1;
        Type_Material_reboiler = 1;
        pressure_reboiler = 1;
        Reboiler_total_cost = Cost_reboiler*Pipe_length_reboiler*Type_Material_reboiler*pressure_reboiler;
        % cost of utilities
        Chilled_water_cost = ((Aspen.Tree.FindNode("\Data\Blocks\B2\Output\COND_DUTY").Value)*4.1868)*31536000*0.0000000009258;
        Steam_Cost = ((Aspen.Tree.FindNode("\Data\Blocks\B2\Output\REB_DUTY").Value)*4.1868)*0.000000004607*31536000;
        
        TAC(1) = (Cost_column + Condenser_total_cost + Reboiler_total_cost)*Lang_F*1.14*1.1906/10;
        TAC(2) = Steam_Cost + Chilled_water_cost;
          
    else
        TAC(1) = inf;
        TAC(2) = inf;
        
    end
    
Aspen.Quit();
end

Best Answer

I don't know where your objective function creates complex values, though I suspect that one or more of your logarithm calls has a negative number as an argument. You can fix this problem by making your code more robust. Test all inputs to logarithms (or square roots or similar) to ensure that they are not negative before applying the functions. Or, if you can, impose bounds or linear inequality constraints to ensure that negative arguments do not get passed. Unfortunately, gamultiobj does not satisfy nonlinear inequality constraints at intermediate iterations, so you cannot fix the problem by imposing nonlinear constraints.

Alan Weiss

MATLAB mathematical toolbox documentation

Related Solutions

MATLAB: How can get the value for each time step for a variable inside of a function

Hi,

you try this code (all in one file as nested function). The values you want to have in every iteration are now added to the solution and also saved in the results table. This should be what you want.

Result = main
function Result = main
%Initial conditions
Wads=0.045;
Tads=80;
Wdes=0.035;
Tdes=27;
Teva=7;
Tcond=27;
Mweva=0.65;         
Initial=[Wads Tads Wdes Tdes Mweva Teva Tcond 0 0 0 0];           
tspan=[1:1:800];
opts = odeset('RelTol',1e-6,'AbsTol',1e-6);
[t,Soln]=ode45(@(t,Soln)ODEdw(t,Soln),tspan,Initial,opts);
colNames = {'Time','Wads','Tads','Wdes','Tdes','Mweva', 'Teva','Tcond',...
    'Tcwaout', 'Thwdout', 'Tchwout', 'Tcwcout'};
Result = array2table([tspan',Soln],'VariableNames',colNames);
function [dYdt] =ODEdw(~,Soln)
Ea=4.2*10^4;         %Activation energy of surface diffusion, (J/mol)
R=8.314;             %Ideal gas constant, (j/mol.K)
Dso=2.54*10^-4;       %Pre-exponential constant, (m^2 S^-1)
Qs=2.8*10^6;         %Heat of adsorption, (J/kg)
%%%%%%%%%%%Operating conditions%%%%%%%%%%%%%%%%%%%%%%%%%%%%
Thwdin=85;            %Inlet temperature of hot water in desorber, (oC)
Tcwain=27;            %Inlet temperature of cooling water in adsorber, (oC)
Tcwcin=27;            %Inlet temperature of cooling water in condenser, (oC)
Tchwin=14;            %Inlet temperature of chilling water in evaporator, (oC)
mcwa=8/60;            %Mass flow rate of cooling water in adsorber, (kg/s)
mcwc=20/60;           %Mass flow rate of cooling water in condenser, (kg/s)
mchw=1.6/60;          %Mass flow rate of chilling water in evaporator, (kg/s)
mhwd=7/60;            %Mass flow rate of hot water in desorber, (kg/s)
%%%%%%%%%Physical and thermal properties of adsorbent%%%%%%%%%%
Cps=924;              %Specific heat capacity of silica gel, (J/kg.K)
Ms=9;                 %Mass of silica, (kg)
Rp=5.6*10^-4;         %Radious of silica gel particle, (m)
ps=700;              %density of silica gel, (kg/m^3)
Por=0.3;              %Porosity of silica gel,
%%%%%%Physical and thermal properties of adsorbate%%%%%%%%%%%%%
Cpw=4200;             %Specific heat capcity of water, (J/kg.k)
Cpv=1900;             %Specific heat capacity of water vapor (J/kg.K)
M=18.02;              %Molar mass of water, (g/mol)
Lv=2500*10^3;         %Lantent heat of vaporization (J/kg) 
%%%%%%%%%Physical and thermal Properties of Condenser%%%%%%%%%%%%%
Acond=5.76;            %Surface area of condenser, (m^2)
Mhexcond=19.87;        %Mass of heat exchanger (Condenser), (kg)
Ucond=486.87;          %Heat transfer coefficient of condenser, (W/m^2.K)
UAcond=Acond*Ucond;
Mwcond=1.0;         %Mass of water in Condenser (kg)
%%%%%%%%%%Physical and thermal properties of adsorber/desorber   %%%%%%%
Mhex=65;             %Mass of heat exchanger (Adsorber/desorber), (kg)
Cphex=386;           %Heat capacity of heat excahgner, (J/kg.K)
Aad=2.11;            %Surface area of adsorber/desorber, (m^2)
Uads=189.60;         %Heat transfer coefficient of adsorber, (W/m^2.K)
Udes=203.99;         %Heat transfer coefficient of desorber, (W/m^2.K)
UAads=Aad*Uads;
UAdes=Aad*Udes;
Vt=0.5;              %volume of adsorber/desorber tank, (m^3)
%%%%%%%%%Physical and thermal Properties of Evaporator%%%%%%%%%%%%%%
Aeva=0.34;           %Surface area of evaporator, (m^2)
Mhexeva=16.1;        %Mass of heat exchanger (Evaporator), (kg)
Ueva=302.58;         %Heat transfer coefficient of evaporator, (W/m^2.K)
UAeva=Aeva*Ueva;
Wads=Soln(1);    
Tads=Soln(2);  
Wdes=Soln(3);    
Tdes=Soln(4);
Mweva=Soln(5);
Teva=Soln(6);
Tcond=Soln(7);
Kads=((15*Dso)/(Rp).^2)*exp(-Ea/(R*(Tads+273.16)));   %Overall mass tarsnfer coeffcient of adsorber

Pwa=133.32*exp(18.3-(3820/((Teva+273.16)-46.1))); % Saturated vapour pressure of waterm (vapour) at adsorbent temperature, (Pa)

Psga=133.32*exp(18.3-(3820/((Tads+273.16)-46.1))); % Saturated vapour pressure of water at adsorbent temperature, (Pa)

Weqa=0.346*(Pwa/Psga)^0.625;
Aads=(Kads*(Weqa-Wads));
TLads=(Ms*(Cpw+Cpw*Wads)+Mhex*Cphex); %Left hand side of adsorber equation
Tcwaout=Tads+(Tcwain-Tads)*exp((-UAads)/(mcwa*Cpw));
   
Kdes=((15*Dso)/(Rp).^2)*exp(-Ea/(R*(Tdes+273.16)));   %Overall mass tarsnfer coeffcient of adsorber
Pwd=133.32*exp(18.3-(3820/((Tcond+273.16)-46.1))); % Saturated vapour pressure of waterm (vapour) at adsorbent temperature, (Pa)
Psgd=133.32*exp(18.3-(3820/((Tdes+273.16)-46.1))); % Saturated vapour pressure of water at adsorbent temperature, (Pa)
Weqd=0.346*(Pwd/Psgd)^0.625;
Ades=(Kdes*(Weqd-Wdes));
TLdes=(Ms*(Cps+Cpw*Wdes)+Mhex*Cphex); %Left hand side of desorber equation
Thwdout=Tdes+(Thwdin-Tdes)*exp((-UAdes)/(mhwd*Cpw));
  
TLeva=(Mweva*Cpw+Mhexeva*Cphex); %Left hand side of evaporator equation

Tchwout=Teva+(Tchwin-Teva)*exp((-UAeva)/(mchw*Cpw));
  
TLcond=(Mwcond*Cpw+Mhexcond*Cphex); %Left hand side of evaporator equation
Tcwcout=Tcond+(Tcwcin-Tcond)*exp((-UAcond)/(mcwc*Cpw));
dYdt=[Kads*(Weqa-Wads);((Qs*Ms*Aads)+(Ms*Cpv*Aads*(Teva-Tads))+mcwa*Cpw*(Tcwain-Tcwaout))/TLads;
    Kdes*(Weqd-Wdes); ((Qs*Ms*Ades)+(mcwa*Cpw*(Thwdin-Thwdout)))/TLdes; 
    -Ms*((Kads*(Weqa-Wads))+(Kdes*(Weqd-Wdes)));((-Lv*Ms*Aads)+Ades*Ms*Cpw*(Tcond-Teva)+mchw*Cpw*(Tchwin-Tchwout))/TLeva;
    (Ades*Ms*Cpv*(Tdes-Tcond)+(Lv*Ms*Ades)+mcwc*Cpw*(Tcwcin-Tcwcout))/TLcond; Tcwaout; Thwdout; Tchwout; Tcwcout];
end
end

Best regards

Stephan

MATLAB: Error: “Not enough input arguments”

You cannot run the objective function directly: you need to run a function such as the supplied Opt* function which sets up the conditions for everything to be called.

Best Answer

Related Solutions

MATLAB: How can get the value for each time step for a variable inside of a function

MATLAB: Error: “Not enough input arguments”

Related Question