TRANSFORM
A Modelica library for system-level dynamic simulation of nuclear and other thermal-hydraulic energy systems — fluid networks, heat transfer, heat exchangers, nuclear kinetics, media, and controls in one reconfigurable package. Started at ORNL in 2017, still moving, Apache-2.0.
Active·since — views
What it is. TRANSFORM — TRANsient Simulation Framework of Reconfigurable Models — is a Modelica library for modeling thermal-hydraulic energy systems and other multi-physics systems. I started the public repo at ORNL on 2017-08-14 (the DOE software record is dated 26 Sep 2017) and it has never really stopped — still active as of August 2026. It is Apache-2.0, developed against Dymola, and built on the Modelica Standard Library 4.0.0.
Why. Whole-system dynamics. A reactor’s primary loop, heat exchangers, kinetics, and controls are one coupled problem, and Modelica treats it that way: models are equations, not procedures, so you connect components and let the tool assemble and solve the system. “Reconfigurable” is the point of the name — swap a pump model, add a loop, change the working fluid, and the rest of the model comes along.
What’s in the library
The top-level sub-packages, as they sit in TRANSFORM/:
| Package | What’s there |
|---|---|
Fluid |
The core: fluid networks, pipes, volumes, machines (pumps, including homologous-curve turbo pumps), and their examples |
HeatAndMassTransfer |
Conduction, convection, and mass-transfer components |
HeatExchangers |
Heat exchanger models built from the fluid and heat-transfer pieces |
Nuclear |
Reactor kinetics and nuclear-specific components |
Media |
Fluid property packages |
PeriodicTable |
Element data |
Electrical, Mechanics |
The non-thermal ends of a plant model |
Blocks, Controls, Math |
Signal blocks, controllers, and math helpers |
Types, Units, Icons, Utilities |
Support: types, unit definitions, icons, utilities |
Examples, UsersGuide |
Worked examples and the in-library guide |
Resources |
Images, external includes, a compiled library, data, Python helpers, and reference results |
Regression checks live alongside: the README’s “check that the library is
working” step is to run the runAll_*.mos scripts, which drive the unit tests
against reference results under Resources/ReferenceResults. Fair warning
from the README itself: it takes a while, and you are allowed to make it stop.
The tag history tells the version story in miniature: v0.1-beta through
v0.4-beta, then a Before_MSL_4.0 tag marking the move to Modelica Standard
Library 4.0, and package.mo now declares version 1.0.
Where it has been used
Publications on this site built on TRANSFORM:
- Demonstration of the Advanced Dynamic System Modeling Tool TRANSFORM in a Molten Salt Reactor Application via a Model of the Molten Salt Demonstration Reactor — Nuclear Technology, 2019
- Status Report on the MSRE Transform Model for Thermal-Hydraulic Benchmarking — ORNL/TM-2019/1359
- A Frequency Response Approach to Model Validation for the Compact Integral Effects Test Facility in TRANSFORM — NURETH-18, 2019
- TRANSFORM – A Vision for Modern Advanced Reactor System-Level Modeling and Simulation Using Modelica — ANS Winter Meeting, 2020
- TRANSFORM: Description and Applications — poster, ORNL Software and Data Expo, 2021
- Dynamic Thermal Hydraulic Modeling TRANSFORM-ed — presentation, 2016
- Thermo-Fluid Modeling Framework for Supercomputer Digital Twins: Part 1, Demonstration at Exascale and Part 2, Automated Cooling Models — America Modelica Conference, 2024
- Modeling HFIR’s Steady State Heat Transfer Code with Modelica — poster, 2025
Reactors first, then data-center cooling and a research reactor: the same fluid and heat-transfer components carry over. The repo’s Publications wiki page keeps the full list of work built on it.
Related
- Training. The TRANSFORM-Training repo is the place to start if you want to learn the library rather than read it.
- Demo reel. TRANSFORM — Get Results! (first published 2019).
- Videos. Two training videos, A Simple ODE and Simple Heat Transfer Loop, and simulation data on a T-s diagram, all on the ORNL-VARSA channel.
- Testing. DSTF is the regression harness I built for exactly this kind of library, with Dymola and OpenModelica among its backends.
Citing it. Greenwood, M. S. TRANSFORM — TRANsient Simulation Framework of Reconfigurable Models. Computer software. USDOE, 26 Sep. 2017. doi:10.11578/dc.20171025.2022.