OpenSeesPy (Linux)

Common errors

• ModuleNotFoundError: No module named 'openseespy'

  cause The `openseespylinux` package was not installed, or the Python environment where it was installed is not active, or an incompatible Python version is used.
  fix Activate the correct Python environment (Python 3.12 or newer) and run `pip install openseespylinux`.

• ImportError: DLL load failed while importing opensees

  cause Attempting to install or run `openseespylinux` on a non-Linux operating system (e.g., Windows, macOS). This package is Linux-specific.
  fix Use a Linux environment (native, WSL, Docker, or VM) for `openseespylinux`. For other OS, seek platform-specific distributions or build OpenSeesPy from source.

• OSError: [Errno 8] Exec format error: '/path/to/openseespy/opensees.cpython-312-x86_64-linux-gnu.so'

  cause This error occurs when trying to run the Linux-compiled binaries (e.g., an `.so` file) on a non-Linux system or a system with an incompatible architecture.
  fix Ensure you are running the `openseespylinux` package strictly within a compatible Linux environment matching the architecture (e.g., x86_64).

• AttributeError: module 'openseespy' has no attribute 'model'

  cause Incorrect import statement. The `openseespy` module itself does not expose the OpenSees commands directly; they are nested in the `opensees` submodule.
  fix Change your import from `import openseespy` to `import openseespy.opensees as ops` to correctly access the OpenSees command API.

Warnings

• breaking The `openseespylinux` package is strictly for Linux operating systems. Attempting to install or run it on Windows or macOS will result in `ImportError` or `OSError` due to incompatible binaries.
  Fix: Ensure you are using a Linux environment (native, WSL, Docker, or VM) for installation and execution. For other operating systems, consider `openseespy` (if available for your OS) or building from source.
• breaking `openseespylinux` requires Python 3.12 or newer. Installing with older Python versions will likely lead to `ModuleNotFoundError` or other runtime `ImportError` issues.
  Fix: Verify your active Python version (`python --version`) and ensure it is 3.12 or greater. Use a virtual environment to manage Python versions if necessary.
• gotcha The standard and correct way to access OpenSees commands is `import openseespy.opensees as ops`. A common mistake is to simply use `import openseespy`, which does not expose the command API directly.
  Fix: Always use `import openseespy.opensees as ops` to ensure access to all OpenSees commands (e.g., `ops.model()`, `ops.node()`).
• gotcha It is critical to call `ops.wipe()` at the beginning of any new model definition or before running multiple independent analyses within the same Python script. Failure to do so can lead to unintended interactions and incorrect results from previously defined model components.
  Fix: Always include `ops.wipe()` as the very first command when defining a new OpenSees model.

Install

• pip install openseespylinux Install for Linux

Imports

• ops
  wrong:

  import openseespy

  correct:

  import openseespy.opensees as ops

  The core OpenSees commands are exposed via the `opensees` submodule, aliased as `ops` by convention.

Quickstart

This example demonstrates a basic static analysis of a simple truss element, including model definition, material/element assignment, boundary conditions, loading, analysis, and result retrieval. It's crucial to call `ops.wipe()` before defining a new model.

import openseespy.opensees as ops

# 1. Start a new model (2D, 3 DoF per node)
ops.wipe()
ops.model('basic', '-ndm', 2, '-ndf', 3)

# 2. Define a uniaxial elastic material (tag 1, E=3000)
ops.uniaxialMaterial('Elastic', 1, 3000.0)

# 3. Define nodes
ops.node(1, 0.0, 0.0)
ops.node(2, 10.0, 0.0)

# 4. Define boundary conditions (fixed at node 1)
ops.fix(1, 1, 1, 1)

# 5. Define an elastic truss element (tag 1, nodes 1-2, Area=1.0, material tag 1)
ops.element('Truss', 1, 1, 2, 1.0, 1)

# 6. Define a time series (constant) and load pattern
ops.timeSeries('Constant', 1)
ops.pattern('Plain', 1, 1)
ops.load(2, 0.0, -100.0, 0.0) # Apply 100 units downward load at node 2

# 7. Define analysis parameters
ops.integrator('LoadControl', 0.1)
ops.numberer('RCM')
ops.constraints('Plain')
ops.system('BandGeneral')
ops.algorithm('Newton')
ops.analysis('Static')

# 8. Perform analysis in 10 steps
ops.analyze(10)

# 9. Get results (Y-displacement of node 2)
disp_y = ops.nodeDisp(2, 2)
print(f"Y-displacement at node 2: {disp_y}")

# 10. End model and clear memory
ops.wipe()