This bug is older than 2023, I have it from time to time. Restarting always works, but that's not what you want do when you're in the middle of something.

One of my suspicions is that it happens when the display settings change. For example, when you disconnect an external monitor from a laptop. 

Another possibility is that it is related to the load on the system (applications running in parallel, number and history of mservers managed by the Maple GUI or the time and history since last logon). 

In both cases it is related to the operating system and may not be a programming bug, but something that depends on Microssoft and/or the OpenJDK platform.

Your observation (new to me) that it depends on maximising the GUI Window points rather to the first susspicion.

@acer
Yes, exactly!

@Maxie 

The model I have send to you must have changed its state when it was saved.

In the model I have send to you to make it simulate, try chaning the EC to:

This should assemble and allow you to inspect the model.

As I have said the model does not assemble correctly. You should fix this first.

4_fix-3.msim

Here is another good video https://www.youtube.com/watch?v=4c0dbvAMrAU on custom contact components. I would try to combine it with a classical analytical formula for beam deflection.

To start I would use the deflection for a "Simply Supported, Intermediate Load" as given here

https://mechanicalc.com/reference/beam-deflection-tables

(I cannot guarante if these formulas are correct.)

@Maxie 

I have fixed your model in the sense that its simulating.

At a frist glance the rails and the sleepers are not assembled as you intended.

Furthermore, the axle falls off the rails.

You cannot use a single contact element (rectangle) for the entire flexible beam to realistically describe a traveling load. As you have done it the rail already deforms when the load is above the sleeper.

Overall the problem you have choosen is at the limit of the components of MapleSim libraray. I think a solution is possible with custom components.

If you are entitled consider also contacting Maplesoft support for advice.

4_fix.msim

@acer You are correct. A thetrahedron has 4 surfaces. 5 was from my first answer which I had to correct.

z<=1 and y<=z eliminate y<=1 (which I will do now in my update above).

In this question you will find an elegant way from the user Kitonum to plot the bounding surface of a cube which is

plots:-implicitplot3d(max(-x,x-1,-y,y-1,-z,z-1), x=-0.5..1.5, y=-0.5..1.5, z=-0.5..1.5, style=surface, axes=normal, grid=[100,100,100]);

The three inequalities (i.e. all points within the bounding surface and including the bounding surface) describing the cube as solid are

0<=x <= 1
0<=y <= 1
0<=z <= 1

This that what you are looking for?

@Maxie 

Without model its difficult to tell why forces are constant. If this is related to a question that I have seen but  has disappeared, consider adding it to this thread.

Here are two models which might help you with your problem.

The first is a (rigid) beam under a moving load. The second is not available for immediate download and you have to contact Maplesoft but its worth a try.

And: A rail with multiple (>2) sleepers must be overdetermined. What exactly do you mean with "the rail is supported by multiple sleepers without over-constraint".

@mmcdara 
Your idea is worth discussing. I have seen that it (screen shot instead of code) just happend again.

Perhaps a post would be better to gather more ideas.

You have to be more specific what you want to analyse.

If it is a mechanical problem you want to analyse:

The load case (e.g. bending) and the geometry would be helpfull.

Do you have drawings or a sketch?

It would be nice if convert/unit would offer

1. symbols as yours for degrees minutes and seconds
2. a compound output as yours

Here is what is possible with 2023

(which represents a silent improvement over 2022 where trunc an floor did not work on expressions with units.

Thank you Maplesoft and please continue)

Download degminsec.mw

What version do you use?

Download total_PE.mw

@Kitonum 
I have been too hasty. x >= 0 leaves of course two choices for T2. 👍

@Kitonum 

Math put that way in only 2 lines is really nice.
S<=0 seems to be a quite broad definition for solids with a closed surface S=0 as a boundary. 

However, extending your method of defining an intersection with inequalities and max to polyhedrons does not work straight away. I tried to plot a cube and an infinite slice with planes without immediate success. At least with one plane it can be used to chop of the head of an egg.

z^2/9 + (x^2 + y^2)/(4*(1 - z/5)) - 1;
plots:-implicitplot3d(max(%, z - 2), x = -3 .. 3, y = -3 .. 3, z = -3 .. 4, style = surface, color = red, grid = [100, 100, 100]);

Thanks again.

@acer 
Thanks for the clarification

@acer 

Vertical adjustments become tricky. 

If I understand correctly, the question about linking such a user defined symbol to a name should be asked separately.
I am never quite sure when to branch off.

Thank you.