OpenSees-Tcl & OpenSeesPy

OpenSees-Tcl & OpenSeesPy#

OpenSees Interpreters

There are two main interpreter-based versions of OpenSees:

  • OpenSees-Tcl, which uses the Tcl scripting language and is distributed as standalone executables.

  • OpenSeesPy, which is a Python library that extends Python with OpenSees-specific commands.

At the core, both are compiled from the same source code and perform the same types of structural and geotechnical simulations. The difference lies in how they’re executed, which impacts your workflow on HPC systems, in Jupyter, and when designing automated pipelines.

Quick Comparison

OpenSees-Tcl runs as an external executable—great for stable batch scripts and domain-decomposed OpenSeesSP jobs—while OpenSeesPy runs inside Python, letting you interrogate and steer the model during execution, integrate with scientific Python, and smoothly scale via Tapis to large parametric studies (with OpenSeesMP or mpi4py). Use OpenSees-Express for quick sequential jobs and first-time runs; move to Jupyter for interactive development; and submit production jobs with Tapis for automation, provenance, and scale.

How they run#

OpenSees-Tcl

This version is a self-contained executable application that bundles the Tcl interpreter. You run it by calling an OpenSees command at the terminal or in a job script, typically providing your input file as a command-line argument. For example:

OpenSees model.tcl

When no input file is given, OpenSees runs in interactive mode, prompting you for commands one at a time. When an input file is given right after the command, internally, OpenSees “sources” your Tcl script — meaning it reads and executes each command inside the file using its embedded Tcl interpreter.

Executables like OpenSees, OpenSeesMP, and OpenSeesSP are separate binaries. You choose the one that fits your analysis (sequential, parallel with shared memory, or parallel with distributed memory).

OpenSeesPy

This version is a Python library, not a standalone executable. You run OpenSeesPy by invoking Python, which then loads your script that imports the OpenSeesPy module:

import openseespy.opensees as ops

So instead of calling a specialized OpenSees program, you run:

python model.py

where model.py is a standard Python script that builds your model and analysis using OpenSeesPy’s functions. When no input file is given, python runs in interactive mode, prompting you for commands one at a time.

Because OpenSeesPy sits inside Python, it benefits from Python’s full ecosystem for data processing, visualization, and automation. However, support for OpenSeesMP and OpenSeesSP features in OpenSeesPy can vary by platform, so it’s recommended to test parallel capabilities explicitly on Jupyter Hub vs the HPC environment.

This setup — where an application either wraps its own interpreter (like OpenSees-Tcl) or extends an existing one (like OpenSeesPy) — is standard in computational research. Most HPC applications work this way:

  • You run a command at the CLI, optionally pass an input file, and the program processes commands line by line.

  • This direct use of the command-line interface (CLI) is essential on HPC systems. It gives you complete control, enables robust automation, and allows scaling analyses across thousands of cores or parameter sets, all without relying on graphical interfaces.

  • And in truth, almost all programs are run this way under the hood — whether you type the command in a terminal, click a “Run” button in a GUI, or submit a job through a web portal, it ultimately launches a process that runs the same core command-line invocation.

Summary comparison#

Aspect

OpenSees-Tcl

OpenSeesPy

Interpreter Language

Tcl

Python

Execution Method

Run via OpenSees executable (OpenSees, OpenSeesMP, etc.)

Run Python script with import openseespy.opensees as ops

File Type

.tcl script

.py script

Input File Handling

Passed as command-line argument; sourced internally

Python runs the script; functions call OpenSeesPy commands

Executable Variants

Separate binaries: OpenSees, OpenSeesMP, OpenSeesSP

Typically a single package; may or may not support MP/SP

Interactive Mode

Available when run with no arguments

Available when Python run with no script

Source Code

Same for both versions

Same for both versions

Usage Style

Terminal/CLI call to executable

Run Python script through Python interpreter

Import Required?

No

Yes (import openseespy.opensees as ops)

Recommended For

Legacy scripts, direct CLI usage

Python workflows, scripting integration, data handling
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