Introduction
Plug-in architecture
compas_fea2 implements a plug-in architecture. The compas_fea2 main
package only defines the general API for a Finite Element Analysis, while the
actual implementation in the a specific backend is done in the corresponding
plug-in, whcih is registered and the beginning of the analysis. Once the analysis
is complente, the results are recorded in a SQL database and can be accessed by
the user through the SQL wrapper provided by compas_fea2, by his/her own
SQL statements or through an external interface.
Workflow
The image below describes a general FEA workflow:
Collaboration Workflow
The aim of compas_fea2 is to create a common platform for FEA that can be shared
across disciplines and software. This is achieved by standardizing the API for
the creation and analysis of an FE model, and by serializing models, problems
and results in a common database that can be easly shared.
The two images below show the general collaboration workflow and a specific example of a structural engineer using rhino and abaqus collaborating with an acoustic engineer using blender and ansys:
Units
Before starting any model, you need to decide which system of
units you will use. compas_fea2 has no built-in system of units.
Warning
Units consistency
All input data must be specified in consistent units.
Do not include unit names or labels when entering data in compas_fea2.
Some common systems of consistent units are shown in the table below:
Quantity |
SI |
SI (mm) |
US Unit (ft) |
US Unit (inch) |
|---|---|---|---|---|
Length |
m |
mm |
ft |
in |
Force |
N |
N |
lbf |
lbf |
Mass |
kg |
tonne (103 kg) |
slug |
lbf s2/in |
Time |
s |
s |
s |
s |
Stress |
Pa (N/m2) |
MPa (N/mm2) |
lbf/ft2 |
psi (lbf/in2) |
Energy |
J |
mJ (10−3 J) |
ft lbf |
in lbf |
Density |
kg/m3 |
tonne/mm3 |
slug/ft3 |
lbf s2/in4 |
In case you do not want to follow a predefined system, you need to be consistent with your units assignemnts. Below there are some exmple of correct choices of units:
MASS |
LENGTH |
TIME |
FORCE |
STRESS |
ENERGY |
|---|---|---|---|---|---|
kg |
m |
s |
N |
Pa |
J |
kg |
mm |
ms |
kN |
GPa |
kN-mm |
ton |
mm |
s |
N |
MPa |
N-mm |
lbf-s²/in |
in |
s |
lbf |
psi |
lbf-in |
slug |
ft |
s |
lbf |
psf |
lbf-ft |
The order of magnitude expected for different properties is shown below:
Type |
Commonly used unit |
SI value |
SI-mm value |
Multiplication factor from commonly used to SI-mm |
|---|---|---|---|---|
Stiffness of Steel |
210 GPa |
210∙10^9 Pa |
210000 MPa |
1000 |
Stiffness of Concrete |
30 GPa |
30∙10^9 Pa |
30000 MPa |
1000 |
Density of steel |
7850 kg/m3 |
7850 kg/m3 |
7.85∙10^-9 tonne/mm3 |
10^-12 |
Density of concrete |
2400 kg/m3 |
2400 kg/m3 |
2.4∙10^-9 tonne/mm3 |
10^-12 |
Gravitational constant |
9.81 m/s2 |
9.81 m/s2 |
9810 mm/s2 |
1000 |
Pressure |
1 bar |
10^5 Pa |
0.1 MPa |
10^-1 |
Absolute zero temperature |
-273.15 ̊C |
0 K |
C and K both acceptable |
|
Stefan-Boltzmann constant |
5.67∙10-8 W∙m-2∙K-4 |
5.67∙10-11 mW∙mm-2∙K-4 |
0.001 |
|
Universal gas constant |
8.31 J∙K-1∙mol-1 |
8.31∙103 mJ∙K-1∙mol-1 |
1000 |