Material wave propagation Speed and Courant number is not properly computed in Explicit Dynamics when the model is in mmgs units.
Attached the same analysis written in two different unit systems. One MKs , the other in mmgs. Both deliver same material wave speed (they shouldn’t [m/s] & [mm/s]) and lead to different Courant numbers (Should be the same).
As a result, one frd (MKs) is much larger than the other (mmgs).
10.E+03
--- Lock the Penduls mass moment of initia
--- + movement in Z-plane
node,dir,fact,node,dir,fact ......... = 0
Equation
2
5,2,1.,3,2,-1.
2
5,3,1.,3,3,-1.
Lock the pendul arm at the center of pendul
3
10,1,1.,9,1,-0.5,19,1,-0.5
3
10,2,1.,9,2,-0.5,19,2,-0.5
3
10,3,1.,9,3,-0.5,19,3,-0.5
Step, Nlgeom, Inc=11000
*Dynamic, Explicit
0.01, 0.5, 1E-04, 0.005
*Boundary, op=New
Origon, 1, 3, 0.
PendulBack, 3, 3, 0.
*Dload, op=New
Pendul, Grav, 9.820, 0, -1, 0
*Node file
RF, U, V
El file
S, E, ENER
End step
`
10.E+06
--- Lock the Penduls mass moment of initia
--- + movement in Z-plane
node,dir,fact,node,dir,fact ......... = 0
Equation
2
5,2,1.,3,2,-1.
2
5,3,1.,3,3,-1.
Lock the pendul arm at the center of pendul
3
10,1,1.,9,1,-0.5,19,1,-0.5
3
10,2,1.,9,2,-0.5,19,2,-0.5
3
10,3,1.,9,3,-0.5,19,3,-0.5
Step, Nlgeom, Inc=11000
*Dynamic, Explicit
0.01, 0.5, 1.E-04, 0.005
*Boundary, op=New
Origon, 1, 3, 0.
PendulBack, 3, 3, 0.
*Dload, op=New
Pendul, Grav, 9820, 0, -1, 0
*Node file
RF, U, V
El file
S, E, ENER
End step`
(Largest computation time is no more than 1 minute)
Material wave propagation Speed and Courant number is not properly computed in Explicit Dynamics when the model is in mmgs units. Attached the same analysis written in two different unit systems. One MKs , the other in mmgs. Both deliver same material wave speed (they shouldn’t [m/s] & [mm/s]) and lead to different Courant numbers (Should be the same). As a result, one frd (MKs) is much larger than the other (mmgs).
Details on Post: https://calculix.discourse.group/t/dynamic-explicit/1897/24 Files:
` Pendul dimension m, kilogram, second Node 1, 0.151421356, -0.151421356, -0.0025 2, 0.151421356, -0.141421356, -0.0025 3, 0.151421356, -0.131421356, -0.0025 4, 0.141421356, -0.131421356, -0.0025 5, 0.131421356, -0.131421356, -0.0025 6, 0.131421356, -0.141421356, -0.0025 7, 0.131421356, -0.151421356, -0.0025 8, 0.141421356, -0.151421356, -0.0025 9, 0.141421356, -0.141421356, -0.0025 10, 0.141421356, -0.141421356, 0.0 11, 0.151421356, -0.151421356, 0.0025 12, 0.151421356, -0.141421356, 0.0025 13, 0.151421356, -0.131421356, 0.0025 14, 0.141421356, -0.131421356, 0.0025 15, 0.131421356, -0.131421356, 0.0025 16, 0.131421356, -0.141421356, 0.0025 17, 0.131421356, -0.151421356, 0.0025 18, 0.141421356, -0.151421356, 0.0025 19, 0.141421356, -0.141421356, 0.0025 20, 0.0, 0.0, 0.0 Element, Type=C3D8, Elset=Pendul 1, 1, 2, 9, 8, 11, 12, 19, 18 2, 8, 9, 6, 7, 18, 19, 16, 17 3, 2, 3, 4, 9, 12, 13, 14, 19 4, 9, 4, 5, 6, 19, 14, 15, 16 Nset, Nset=PendulBack 1, 2, 3, 4, 6, 7, 8, 9 Nset, Nset=Origon 20 Material, Name=Steel Density 7800 Elastic 210E+09, 0.3 Solid section, Elset=Pendul, Material=Steel --- Using a stiff spring as connecting rod Element, Type=springa, Elset=Espring 200, 10, 20 Spring, Elset=Espring
10.E+03 --- Lock the Penduls mass moment of initia --- + movement in Z-plane node,dir,fact,node,dir,fact ......... = 0 Equation 2 5,2,1.,3,2,-1. 2 5,3,1.,3,3,-1. Lock the pendul arm at the center of pendul 3 10,1,1.,9,1,-0.5,19,1,-0.5 3 10,2,1.,9,2,-0.5,19,2,-0.5 3 10,3,1.,9,3,-0.5,19,3,-0.5 Step, Nlgeom, Inc=11000 *Dynamic, Explicit 0.01, 0.5, 1E-04, 0.005 * Boundary, op=New Origon, 1, 3, 0. PendulBack, 3, 3, 0. *Dload, op=New Pendul, Grav, 9.820, 0, -1, 0 * Node file RF, U, V El file S, E, ENER End step `
` Pendul dimension mm, gram, second Node 1, 151.421356, -151.421356, -2.5 2, 151.421356, -141.421356, -2.5 3, 151.421356, -131.421356, -2.5 4, 141.421356, -131.421356, -2.5 5, 131.421356, -131.421356, -2.5 6, 131.421356, -141.421356, -2.5 7, 131.421356, -151.421356, -2.5 8, 141.421356, -151.421356, -2.5 9, 141.421356, -141.421356, -2.5 10, 141.421356, -141.421356, 0.0 11, 151.421356, -151.421356, 2.5 12, 151.421356, -141.421356, 2.5 13, 151.421356, -131.421356, 2.5 14, 141.421356, -131.421356, 2.5 15, 131.421356, -131.421356, 2.5 16, 131.421356, -141.421356, 2.5 17, 131.421356, -151.421356, 2.5 18, 141.421356, -151.421356, 2.5 19, 141.421356, -141.421356, 2.5 20, 0.0, 0.0, 0.0 Element, Type=C3D8, Elset=Pendul 1, 1, 2, 9, 8, 11, 12, 19, 18 2, 8, 9, 6, 7, 18, 19, 16, 17 3, 2, 3, 4, 9, 12, 13, 14, 19 4, 9, 4, 5, 6, 19, 14, 15, 16 Nset, Nset=PendulBack 1, 2, 3, 4, 6, 7, 8, 9 Nset, Nset=Origon 20 Material, Name=Steel Density 7800.E-06 Elastic 210000., 0.3 Solid section, Elset=Pendul, Material=Steel --- Using a stiff spring as connecting rod Element, Type=springa, Elset=Espring 200, 10, 20 Spring, Elset=Espring
10.E+06 --- Lock the Penduls mass moment of initia --- + movement in Z-plane node,dir,fact,node,dir,fact ......... = 0 Equation 2 5,2,1.,3,2,-1. 2 5,3,1.,3,3,-1. Lock the pendul arm at the center of pendul 3 10,1,1.,9,1,-0.5,19,1,-0.5 3 10,2,1.,9,2,-0.5,19,2,-0.5 3 10,3,1.,9,3,-0.5,19,3,-0.5 Step, Nlgeom, Inc=11000 *Dynamic, Explicit 0.01, 0.5, 1.E-04, 0.005 * Boundary, op=New Origon, 1, 3, 0. PendulBack, 3, 3, 0. *Dload, op=New Pendul, Grav, 9820, 0, -1, 0 * Node file RF, U, V El file S, E, ENER End step`
(Largest computation time is no more than 1 minute)