Simple question about units

[jhwaxx]

Hello,

I´m very new to Abaqus and have a simple question about the units. Is this correct?

When I create the part with "mm"
Material data must be in "MPa"
Density: "g/cm3"
Velocity: "m/s"
Displacement: "mm"
Step Time (explicit): "ms"



the part in "m"
Material: "GPa"
Density: "kg/m3"
Velocity: "m/s"
Displacement: "m"
Step Time: "s"

Thanks


jhwaxx

 

[Drej]

You may be able to use the upper values you quote (I didn't check the consistency), but take great care. Because of its unnatural consistency for time, velocity and acceleration the `mm-kg-N' system should be used with great care in time-dependent analyses. For instance, the time unit is in (s)/((1000)^0.5) and the velocity in m/s*(1000)^0.5! Use kg-metres-N for time-dependency wherever possible is the general rule to avoid (1) modelling complications and (2) strange units i.e. use the lower values you quote.

-- drej --

 

[corus]

Using metres as your units, and creating the model in CAE, can be difficult as CAE doesn't like small numbers to define the geometry. I tend to stick to mm, N, kg, and seconds for all the units. As drej says you have to be careful for modal analyses and dynamic analyses as the density has to be changed to Tonne/mm^3 rather than kg/mm^3. I blame Newton.

corus

 

[andrearrd]

hello,

i use mm - kg - N for the reason that drej just pointed out being that cae doesnt like small dimensions. but why would density be in tonnes /mm^3 and not kg/mm^3?

thank you,
andi

 

[corus]

You use tonnes because a Newton is kg.m/s^2 and you are using mm as your unit of length. The Newton is therefore inconsistent unless you use tonnes as the mass.

corus