RigidPlastic behaviour for moment overload

[simo-11]

Length is 80 m, height is 2 m. Beam/B3-1
Mmax=fy*Wp=fy*b*h*h/4=350 MNm and max impulse moment for 1/60 s is 5.83 MNms
Mass is 1.248 Mkg, Required vertical impulse is 0.208 MNs
Inertia at fixed end is 80*2*7800 * 40*40= 1997 M kg*m*m
Moment at fixed end for static solution is 80*2*7800*40*10=499 MNm
Expected angular acceleration at start is (499-350)/1997 0.0746
i.e. change of angular velocity in 1/60 s step is 0.00124
and angular velocity is after i steps 2:0.00249, 3:0.00373, 4:0.00497,
and vertical velocity at center of body is i0.00124 1/s 40 m
1:0.0496, 2:0.0995, 3:0.149, 4:0.199, ...
For impulses that can be written as (499/60-350/60)/1997=(8.31-5.83)/1997=2.48/1997=0.00124
As moment decreases rotation should start to slow down after about 45 degrees.
math.degrees(math.acos(350/499))=45.46
B3-2 with lowerded density (7800 -> 1000)

For raised fy (350->1000)

For normal density

[simo-11]

Check process like this:

• For overload moment set joint rotation speed using energy principle
• Cutting cases can also be checked. If cutting requires less work than rotation, it should be preferred

[simo-11]

First step goes as expected if we accept that joint reports applied load instead of actual joint force

Next step fails as impulse and force should remain quite same (due to very small displacement)
and angular velocity after step should be about 0.00249.

[simo-11]

After D:\GitHub\Box2D [master ≡ +0 ~3 -0 !]> git commit -a -m"partial fix for #12"
[master a1660db] partial fix for #12
simulation run reasonable well for 2.2 seconds

After that moment goes below loadlimit which causes too large response.
Step from 2.2, timeStep=0.0166667, gravity=-10
velocityIteration: 0
J:VC:0 vB1=-0.230821 -5.51847 -0.134033
J:VC:0 m_impulse=0 0 0
J:VC:0 Cdot=0.686441 -0.236192 0
J:VC:0 impulse=-856678 294768 5.75417e+06
velocityIteration: 1
J:VC:0 vB1=-1.15189 -10.8234 -0.134033
J:VC:0 m_impulse=-856678 294768 5.75417e+06
J:VC:0 Cdot=-0.003811 -0.055313 0
J:VC:0 impulse=4756.13 69030.7 2.75306e+06
velocityIteration: 2
J:VC:0 vB1=-0.239985 -5.40458 -0.135372
J:VC:0 m_impulse=-851922 363799 8.50723e+06
J:VC:0 Cdot=0 0 0
J:VC:0 impulse=-0 -0 -0
velocityIteration: 3
J:VC:0 vB1=-0.239985 -5.40458 -0.135372
J:VC:0 m_impulse=-851922 363799 8.50723e+06

Which blows simulation up.

[simo-11]

static body gets velocity at 2.2 s

[simo-11]

D:\GitHub\Box2D [master ≡ +0 ~1 -0 !]> git commit -a -m"update of wrong body fix for #12"
[master f538df7] update of wrong body fix for #12

Simulation is still not smooth

[simo-11]

Moment goes down to 350 first time at angle of 0.17.
Expected moment is 492 MNm and impulse 8.20 MNms
math.cos(0.17)*499=491.8067986878708

[simo-11]

As reference B3-11 can be used. It is elastic-plastic with 10 Hz frequency.
D:\GitHub\Box2D [master ≡ +0 ~3 -0 !]> git commit -m"added B3-11 for debugging of #12" .\ep\ep\Beam.h
[master de0e3b1] added B3-11 for debugging of #12

[simo-11]

m_mass at t=0.0167

at 2.2 s