inkFEM

An open-source, 2D structural analysis CLI that implements the Finite Element Method to calculate, generate and plot structures made of linear bars.

Quick Tutorial

Structures are defined as plain-text files following the .inkfem input file format. Let's define a simple structure made of two columns, a beam, and a vertical distributed load over the beam like the following:

                 qy = -100 N/cm
                ┌─────┬─────┬─────┬─────┐
                │     │     │     │     │
                │     ▼     ▼     ▼     │
 nodeC (0, 200) O───────────────────────O nodeD (300, 200)
                │                       │
                │                       │
                │                       │
                │                       │
                │nodeA (0, 0)           │nodeB (300, 0)
              ──O──                   ──O──

Define it in a file called structure.inkfem like so:

inkfem v1.1

|nodes|
nodeA -> 0.0    0.0    {dx dy rz}
nodeB -> 300.0  0.0    {dx dy rz}
nodeC -> 0.0    200.0  {}
nodeD -> 300.0  200.0  {}

|materials|
'steel' -> 1.0 20000000 1.0 1.0 25000 40000

|sections|
'ipe_120' -> 14 318 28 53 9

|loads|
fy ld beam 0.0 -100.0 1.00 -100.00

|bars|
# Columns
col1 -> nodeA{dx dy rz} nodeC{dx dy rz} 'steel' 'ipe_120'
col2 -> nodeB{dx dy rz} nodeD{dx dy rz} 'steel' 'ipe_120'
# Beam
beam -> nodeC{dx dy rz} nodeD{dx dy rz} 'steel' 'ipe_120'

Note

To understand how to define structures using the .inkfem file format, read the specs here.

You can plot the structure using the plot command:

$ inkfem plot path/to/structure.inkfem --scale 1.0 --dark

To solve the structure defined in the structure.inkfem file:

$ inkfem solve path/to/structure.inkfem

If the structural analysis process doesn't encounter any error, it'll produce a solution file inside the same directory as the input file with the same name but .inkfemsol extension. In the example above, this would be structure.inkfemsol.

To also write the sliced (preprocessed) structure to a file, you can provide the -p flag:

$ inkfem solve path/to/structure.inkfem -p

This will generate an additional file with the .inkfempre extension containing the information about how the structure has been sliced into finite elements.

Available Flags

Flag	Type	Description	Required	Default
verbose or -v	bool	use verbose output, including elapsed times	no	false
preprocess or -p	bool	save the preprocessed structure into a .inkfempre file	no	false
safe or -s	bool	perform some extra safety checks before proceeding with the resolution	no	false
error or -e	float	maximum displacement error allowed in the resolution	no	1e-5
weight or -w	bool	include the own weight of the bars	no	false

Build & Test

To build the inkfem binary:

$ make build

This creates the inkfem binary at the project's top level. See the Usage section below to learn how to execute the binary program.

To run the tests:

$ make test

Docs

• Go Modules
• Cobra CLI

Code Structure

The code is split into four main packages:

• structure: defines the structure model
• preprocess: implements the preprocessing or slicing of the structure
• process: implements the processing of a sliced/preprocessed structure
• io: reading from .inkfem files and writing to .inkfempreand .inkfemsol files
• plot: drawing SVG files from the .inkfem, .inkfempreand .inkfemsol files
• cmd: the commands available to the CLI