Problem with pdsolve/numeric

Contextualizing:

I created a routine for solving a thermo-mechanical problem. The size of the spatial domain is a function of time and the thermo-mechanical behavior of the structure.

The solution is obtained by discretizing the time domain in n intervals. The thermo-mechanical responses are obtained at each time t[i] =t[i-1]+dt.

The material exhibits elastic and elastoplastic mechanical behavior and thus the problem was divided into two consecutive phases (phase 1 and 2).

The heat problem is nonlinear because the thermal properties are variable (termal conductivity, specific heat, and density).

The problem:

In phase 2, the pdsolve/numeric command returns an error for the solution of the heat conduction equation (equation called pde1). I believe this error is related to the derivative of thermal conductivity k(x1) (piecewise function).

I tested many alternatives (I wrote the pde1 equation in two different ways), I checked the routine many times and I don't understand the reason for the error. With each attempt, the command returns a different error.

Thanks for your attention and help.

Problem.mw

Hello,

I have a nonhomogeneous heat conduction problem, where the thermal conductivity, the density, and the specific heat of the
material are piecewise functions.

The thermal conductivity derivative has a discontinuity that causes a problem in the pdsolve command (see the first test).

To avoid this problem, I did a second test where the product rule was calculated directly.

Is there a better way to deal with this problem?

thank you

problem.mw

I have a PDE system that relates four functions: sht1, svt1, Lt1, Jirt1.

I'm trying to solve this system numerically, but the pdsolve command returns an error (this error does not make sense to me).

Where am I going wrong?

Thanks!

Test.mw

I'm trying to do something very simple, but I can not do it. I would like to fill the chart with colors of my choice.

restart: with (plots):
plots [animate] (plot, [[sqrt (x), sqrt (x) -1], x = 0..t, filled = true, view = [0..20, 0..5]], t = 0..20);

The filled = true option fills the graph with random colors.
I tried to use filled = ["Blue", "Red"], but that does not work.

Any tips?

Thank you

I am encountering problems solving a system of differential equations.

In the attached file, on the first try the boundary conditions are defined in H: = He, resulting in "Error, (in DEtools / convertsys) unable to compute coeff". On the second try, the boundary conditions are defined in H: = He + 0.00000000000000001 and this works.

What is the possible cause of the problem?

Thank you

problem.mw