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Fix #4312 #4522

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Fix #4312 #4522

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caf3eb7
Avoid chattering in Modelica.Fluid.Examples.TraceSubstances.RoomCO2Wi…
HansOlsson Jan 21, 2025
b010701
Better way of avoiding ill-posed problem.
HansOlsson Jan 21, 2025
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28 changes: 12 additions & 16 deletions Modelica/Fluid/Utilities.mo
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Original file line number Diff line number Diff line change
Expand Up @@ -691,7 +691,7 @@ for a smooth transition from y1 to y2.
c := 0.1*Delta0;
end if;
theta0 := (y0d*mu + y1d*eta)/h0;
if abs(theta0 - c) < 1e-6 then
if abs(theta0 - c) < 1e-6*abs(c) then
// Slightly reduce c in order to avoid ill-posed problem
c := (1 - 1e-6)*theta0;
end if;
Expand All @@ -700,22 +700,18 @@ for a smooth transition from y1 to y2.
eta_tilde := rho*eta;
xi1 := x0 + mu_tilde;
xi2 := x1 - eta_tilde;
if xi1 < x0 or xi2>x1 then
// The limits don't make sense, just use linear interpolation
y := (y1-y0)*(x-x0)/(x1-x0) + y0;

a1 := (y0d - c)/max(mu_tilde^2, 100*Modelica.Constants.eps);
a2 := (y1d - c)/max(eta_tilde^2, 100*Modelica.Constants.eps);
const12 := y0 - a1/3*(x0 - xi1)^3 - c*x0;
const3 := y1 - a2/3*(x1 - xi2)^3 - c*x1;
// Do actual interpolation
if (x < xi1) then
y := a1/3*(x - xi1)^3 + c*x + const12;
elseif (x < xi2) then
y := c*x + const12;
else
a1 := (y0d - c)/max(mu_tilde^2, 100*Modelica.Constants.eps);
a2 := (y1d - c)/max(eta_tilde^2, 100*Modelica.Constants.eps);
const12 := y0 - a1/3*(x0 - xi1)^3 - c*x0;
const3 := y1 - a2/3*(x1 - xi2)^3 - c*x1;
// Do actual interpolation
if (x < xi1) then
y := a1/3*(x - xi1)^3 + c*x + const12;
elseif (x < xi2) then
y := c*x + const12;
else
y := a2/3*(x - xi2)^3 + c*x + const3;
end if;
y := a2/3*(x - xi2)^3 + c*x + const3;
end if;
else
// Cubic S0 is monotonic, use it as is
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