Problem definition file format

OpenBeam reads problem definitions from a YAML file, with the format explained in this page. You can also directly jump to see the YAML example files or test and edit them in the online app.

Then, come back to this page when in doubt about how to define a particular element, load, or parameter.

1. Parameters

This optional section allows you to define variables or parameters, to easily parameterize a structure dimensions, loads, etc. Its format is just a YAML map, which each key being converted into a parameter.

Note

Mathematical expressions and formulas can be used in all entries, including the parameters that have been defined formerly. This is an extension of YAML implemented in OpenBeam, making use of mrpt::expr::CRuntimeCompiledExpression which in turn uses the exprtk language.

Example:

# -------------------------------------------------
#  Parameters
# -------------------------------------------------
parameters:
  G: 9.81
  L: 1         # Dimensions of the problem
  P: G * 1000  # External load value

The YAML short format is also supported:

parameters: { G: 9.81, L: 1, P: G * 1000 }

2. Beam sections

This optional section allows you to define short names for beam sections that will be used in more than one element. A mandatory name key must be defined, along with the material and beam section geometry parameters that will be needed by the particular finite element.

Example:

# -------------------------------------------------
# beam sections
# -------------------------------------------------
beam_sections:
- name: IPE200
  E: 2.1e11     # Young module
  A: 28.5e-4    # Area
  Iz: 1940e-8   # Second moment of area in z

3. Geometry: nodes

Each node must be assigned a unique id number, coordinates (in 2D or 3D), and an optinal label, for easy identification of node names in diagrams and animations. In case of tilted planes using nodal coordinates, additional entries rot_x, rot_y and rot_z may be added to especify the roll, pitch, and yaw rotation angles in degrees, respectively. Planar structures only need to specify rot_z.

Example:

nodes:
- {id: 0, coords: [0   , 0], label: A}
- {id: 1, coords: [2*L , 0], label: B}
- {id: 2, coords: [3*L , 0], label: C, rot_z: 45}

4. Geometry: elements

This section defines how many finite elements exist, to which nodes they are attached, and their type.

For the full list of finite elements implemented in this library, along with their type names and mathematical definitions, see Implemented finite elements.

Example:

nodes:
  - {type: BEAM2D_RA, nodes: [0, 1], section: IPE200}
  - {type: BEAM2D_AR, nodes: [1, 2], section: IPE200}

5. Geometry: constraints

This sections lists all the degrees-of-freedom that are constrained such that their displacement is zero (or any other fixed value).

Each YAML map entry must define the node id number (as defined in the node section above) and which DoF are constrained, using these names:

DX, DY or DZ: Translation in one axis only (X,Y,Z).
RX, RY or RZ: Rotation along one axis only (X,Y,Z).
DXDYDZ: All translations are constrained.
RXRYRZ: All rotations are constrained.
DXDY, DXDZ, DYDZ : Translation in two axis is constrained.
DXDYRZ: A very common case in 2D structures: translation in X and Y, and rotation in Z are constrained.
DXRZ: Translation in X and rotation in Z are constrained.
DYRZ: Translation in Y and rotation in Z are constrained.
DXDYRXRZ: Translations in X,Y and rotations in X and Z are constrained (for beams with torsion loads).
ALL or DXDYDZRXRYRZ: All 6 DoFs are constrained.

Note

You do not need to specify constraints in DoFs that are not used by your finite elements. For example, to fix a 2D rod element to ground, you do not need to explicitly specify that the rotation DoFs are zero, since the library will automatically discard the unused DoFs. Though, it is not an error to overspecify those constraints, only a warning will be generated.

Example:

# Constraints
constraints:
  - {node: 0, dof: DXDYRZ}
  - {node: 3, dof: DXDYRZ}
  #- {node: 2, dof: DY, value: 1e-3} # optional value different than zero.

6. Loads on nodes

This sections allows the definition of concentrated forces or torques at particular DoFs of nodes. Each entry must define these keys:

node: The node id as defined in the node section above.
dof: The DoF on which the load is defined. Any of:
- DX, DY, DZ: for forces. Positive values are in the direction of the axes.
- RX (torsion), RY (bending), RZ (bending): for torques.

Example:

# Loads:
node_loads:
  - {node: 2, dof: DX, value: -P}

7. Distributed loads on the elements

Loads which are distributed along the elements.

The element id number is the 0-based index of the elements as defined in the elements section above.

Implemented load type are:

TEMPERATURE: Temperature increment load. Parameters:
- deltaT: Temperature increment (in Celsius degrees).
- NOTE: Temperature coefficient is right now fixed to 12e-6.
DISTRIB_UNIFORM: Uniformly distributed load. Parameters:
- q: Load density value.
- DX, DY (and optionally, DZ): They must form a unit vector specifying the load direction.
TRIANGULAR: Triangular or trapezoidal load. Parameters:
- q_ini, q_end: Load density values at the first and second element nodes.
- DX, DY (and optionally, DZ): They must form a unit vector specifying the load direction.
CONCENTRATED: Concentrated load at a particular point amid the element. Parameters:
- p: Concentrated load value.
- DX, DY (and optionally, DZ): They must form a unit vector specifying the load direction.
- dist: Distance from the first element node.

Example:

element_loads:
  - {element: 0, type: DISTRIB_UNIFORM, q: 2000*G, DX: 0, DY: -1, DZ: 0}