Custom quasi-secondary compressor models report errors

I want to add a make-up port to the controllable mass flow element, but when I run it he gets the error: Cannot find parameter 'area_C'.And I want to be based on adjusting the position of interface C, what should I do.

component controlled_mass_flow_source

% Controlled Mass Flow Rate Source (2P)

% This block represents an ideal mechanical energy source in a two-phase

% fluid network that can maintain a controlled mass flow rate regardless of

% the pressure differential. There is no flow resistance and no heat

% exchange with the environment. The mass flow rate is set by the physical

% signal port M [kg/s]. A positive value causes fluid to flow from port A

% to port B.

% Copyright 2013-2021 The MathWorks, Inc.

nodes

A = foundation.two_phase_fluid.two_phase_fluid; % A:left

B = foundation.two_phase_fluid.two_phase_fluid; % B:right

C = foundation.two_phase_fluid.two_phase_fluid; %

end

inputs

% Mass flow rate

M = {0, 'kg/s'}; % M:left

end

parameters

power_spec = foundation.enum.power_spec.isentropic; % Power added

% 1 - isentropic

% 0 - none

area_A = {0.01, 'm^2'}; % Cross-sectional area at port A

area_B = {0.01, 'm^2'}; % Cross-sectional area at port B

area_C = {0.01, 'm^2'}; % Cross-sectional area at port C

end

% Parameter checks

equations

assert(area_A > 0)

assert(area_B > 0)

assert(area_C > 0)

end

variables (Access = protected)

mdot_A = {0, 'kg/s'}; % Mass flow rate into port A

mdot_B = {0, 'kg/s'}; % Mass flow rate into port B

mdot_C = {0, 'kg/s'}; % Mass flow rate into port C

Phi_A = {0, 'kW' }; % Energy flow rate into port A

Phi_B = {0, 'kW' }; % Energy flow rate into port B

Phi_C = {0, 'kW' }; % Energy flow rate into port C

end

branches

mdot_A : A.mdot -> *;

mdot_B : B.mdot -> *;

mdot_C : C.mdot -> *;

Phi_A : A.Phi -> *;

Phi_B : B.Phi -> *;

Phi_C : C.Phi -> *;

end

if power_spec == foundation.enum.power_spec.isentropic

variables (Access = private, ExternalAccess = none)

u_in_A = {1500, 'kJ/kg'}; % Specific internal energy for inflow at port A

u_in_B = {1500, 'kJ/kg'}; % Specific internal energy for inflow at port B

u_in_C = {1500, 'kJ/kg'}; % Specific internal energy for inflow at port C

u_out_A = {1500, 'kJ/kg'}; % Specific internal energy for outflow at port A

u_out_B = {1500, 'kJ/kg'}; % Specific internal energy for outflow at port B

u_out_C = {1500, 'kJ/kg'}; % Specific internal energy for outflow at port C

end

intermediates (Access = private, ExternalAccess = none)

% Compute change in specific entropy

[Ds_AB, ht_in_A, ht_out_B] = foundation.two_phase_fluid.sources.isentropic_relation( ...

A.p, B.p, u_in_A, u_out_B, mdot_A, area_A, area_B, ...

A.u_min, A.u_max, A.unorm_TLU, A.p_TLU, A.v_TLU, A.s_TLU, A.u_sat_liq_TLU, A.u_sat_vap_TLU);

[Ds_BA, ht_in_B, ht_out_A] = foundation.two_phase_fluid.sources.isentropic_relation( ...

B.p, A.p, u_in_B, u_out_A, mdot_B, area_B, area_A, ...

A.u_min, A.u_max, A.unorm_TLU, A.p_TLU, A.v_TLU, A.s_TLU, A.u_sat_liq_TLU, A.u_sat_vap_TLU);

end

% For logging

intermediates (Access = private)

power = if ge(M, 0), mdot_A*(ht_out_B - ht_in_A) else mdot_B*(ht_out_A - ht_in_B) end; % Power added to fluid flow

end

equations

% Isentropic relation between inflow and outflow

Ds_AB == 0;

Ds_BA == 0;

% Specific total enthalpy for outflow

ht_out_A == convection_A.ht_I;

ht_out_B == convection_B.ht_I;

end

else % power_spec == foundation.enum.power_spec.none

% For logging

intermediates (Access = private)

power = {0, 'kW'}; % Power added to fluid flow

end

end

equations

% Commanded mass flow rate

mdot_A == M;

% Mass balance

mdot_A +mdot_C +mdot_B == 0;

% Energy balance

Phi_A + Phi_B + Phi_C + power == 0;

% Run-time variable checks

assert(A.p >= A.p_min, message('physmod:simscape:library:two_phase_fluid:PressureMinValid', 'A'))

assert(A.p <= A.p_max, message('physmod:simscape:library:two_phase_fluid:PressureMaxValid', 'A'))

assert(A.u >= A.u_min, message('physmod:simscape:library:two_phase_fluid:InternalEnergyMinValid', 'A'))

assert(A.u <= A.u_max, message('physmod:simscape:library:two_phase_fluid:InternalEnergyMaxValid', 'A'))

assert(B.p >= B.p_min, message('physmod:simscape:library:two_phase_fluid:PressureMinValid', 'B'))

%assert(B.p <= B.p_max, message('physmod:simscape:library:two_phase_fluid:PressureMaxValid', 'B'))

assert(B.u >= B.u_min, message('physmod:simscape:library:two_phase_fluid:InternalEnergyMinValid', 'B'))

assert(B.u <= B.u_max, message('physmod:simscape:library:two_phase_fluid:InternalEnergyMaxValid', 'B'))

end

% Internal components that calculate energy convection at ports A and B

components (ExternalAccess = none)

convection_A = foundation.two_phase_fluid.port_convection(flow_area = area_A, length_scale = sqrt(4*area_A/pi));

convection_B = foundation.two_phase_fluid.port_convection(flow_area = area_B, length_scale = sqrt(4*area_B/pi));

end

connections

connect(A, convection_A.port)

connect(B, convection_B.port)

end

% Equate variables for internal components that calculate energy convection at ports A and B

equations

convection_A.mdot == mdot_A;

convection_A.Phi == Phi_A;

convection_B.mdot == mdot_B;

convection_B.Phi == Phi_B;

convection_A.ht_I == convection_B.ht_I;

end

end

Answer 1

[Abhishek Chakram]

Hi 柯,

It looks like you are trying to add a make-up port to a controlled mass flow source component in a Simscape language model. The error message: Cannot find parameter “area_C" suggests that there is a problem with the definition or usage of the parameter “area_C” in your model.

Here are the steps to address the issue and adjust the position of interface C:

• It seems that you already have “area_C” defined in the parameters section of your component. Make sure that it is not commented out or removed accidentally.
• To adjust the position of interface C, you will need to define how the mass flow rate into port C (“mdot_C”) is controlled. This could be done by creating another input similar to `M` for port C or by defining a relationship between “mdot_C” and other variables in the model.
• You will need to add equations that describe the behavior of port C, like how ports A and B are described. This includes mass balance, energy balance, and any specific conditions or constraints for port C.
• If port C also exchanges energy, you might need to add another internal component like “convection_C” for energy convection calculations at port C.

Here is a sample code for the same:

% Add the internal component for Port C
components (ExternalAccess = none)
    convection_C = foundation.two_phase_fluid.port_convection(flow_area = area_C, length_scale = sqrt(4*area_C/pi));
end

% Add the connection for Port C
connections
    connect(C, convection_C.port)
end

% Update the energy convection equations to include Port C
equations
    convection_C.mdot == mdot_C;
    convection_C.Phi  == Phi_C;
end

% Update the energy balance equation to include Port C
equations
    % Energy balance
    Phi_A + Phi_B + Phi_C + power == 0;
end

I hope this helps!

Best Regards,

Abhishek Chakram