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faq [2022/10/26 18:49]
marijn.nijenhuis [3. Changing units] |
faq [2023/11/09 22:30] (current)
marijn.nijenhuis [3. Changing units] |
| * (rotations in radians are independent of length) | * (rotations in radians are independent of length) |
| * moment of inertia (''nprops(i).mominertia''): default unit is kg*m^2, so moment of inertia scales as L^2. | * moment of inertia (''nprops(i).mominertia''): default unit is kg*m^2, so moment of inertia scales as L^2. |
| * forces (''nprops(i).force'', ''nprops(i).force_initial''): default unit is N = 1 kg*m/s^2 so force scales as L. | * forces (''nprops(i).force'', ''nprops(i).force_initial''): default unit is N = kg*m/s^2 so force scales as L. |
| * moments (''nprops(i).moment'', ''nprops(i).moment_initial''): default unit is Nm = 1 kg*m^2/s^2 so moment scales as L^2. | * moments (''nprops(i).moment'', ''nprops(i).moment_initial''): default unit is N*m = kg*m^2/s^2 so moment scales as L^2. |
| * material stiffness properties (''eprops(i).emod'', ''eprops(i).smod''): default unit is Pa = N/m^2 = kg/(m*s^2) so these scale as 1/L. | * material stiffness properties (''eprops(i).emod'', ''eprops(i).smod''): default unit is Pa = N/m^2 = kg/(m*s^2) so these scale as 1/L. |
| * material density (''eprops(i).dens''): default unit is kg/m^3 so density scales as 1/L^3. | * material density (''eprops(i).dens''): default unit is kg/m^3 so density scales as 1/L^3. |
| * cross-sectional dimensions (''eprops(i).dim''): default unit is m so these dimensions scale as L. | * cross-sectional dimensions (''eprops(i).dim''): default unit is m so these dimensions scale as L. |
| * gravitational acceleration (''opt.gravity''): default unit is m/s^2 so acceleration scales as 1/L. | * gravitational acceleration (''opt.gravity''): default unit is m/s^2 so acceleration scales as L. |
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| In other words, if your script assumes meters as the unit for length, and you want to go to millimeters, the ''nodes'' matrix should be multiplied by 10^3. Likewise, the forces should be multiplied by 10^3, the moments by 10^6, the elasticity and shear modulus by 10^(-6), and all other quantities according to the list above. | In other words, if your script assumes meters as the unit for length, and you want to go to millimeters, the ''nodes'' matrix should be multiplied by 10^3. Likewise, the forces should be multiplied by 10^3, the moments by 10^6, the elasticity and shear modulus by 10^(-3), and all other quantities according to the list above. |
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| Note that output values, so numbers you see in the ''out'' structure and in Spavisual, are affected similarly. | Note that output values, so numbers you see in the ''out'' structure and in Spavisual, are affected similarly. |
