One of the main objectives of this project is to develop an open-source fluid-dynamic model with gas quality tracking. Its name is Shimmer ++ and this deliverable serves as a handbook for installation and use, documenting model formulation, database schema, and numerical methods to support reproducible hydrogen-blending and renewable-gas integration studies, while providing the basis for future functional extensions.
Shimmer++ made available on a public GitHub repository. The model is implemented as an efficient C++ solver and structured to performs both steady-state and transient simulations and explicitly handles multi- species transport and admixing at network nodes. Gas thermophysical properties are computed using the GERG-2008 equation of state, enabling accurate evaluation of compressibility and supporting mixtures with up to 21 chemical species.
Designed to complement rather than replace commercial simulators, Shimmer++ emphasizes transparency and user extensibility. It follows a file-based approach without a graphical user interface, but the public GitHub repository provides examples for scripting and integration with external environments such as GIS From a user standpoint, the software adopts a three-layer architecture centred on Network Data Files (NDFs), i.e., SQLite databases storing topology, asset characteristics, boundary conditions, gas properties, and simulation outputs.
A typical workflow involves initializing an NDF, populating it with network data, specifying simulation settings via a lightweight Lua configuration file, running the solver, and post-processing results directly from the updated NDF.
