Reduced-Order Models

The ROM problemtypes write a case for Kratos' RomApplication RomManager: it runs the full-order model (FOM) at a set of sampled parameter values, builds a POD basis from the snapshots, optionally selects a hyper-reduced integration domain (HROM), and tests the reduced models against the FOM at further samples.

There is one ROM problemtype per physics, in the Reduced-order models group of the Problemtype dropdown:

Problemtype	Full-order model	Default nodal unknowns
ROM · Structural Mechanics	Structural Mechanics	DISPLACEMENT_X, _Y (and _Z in 3D)
ROM · Convection-diffusion	Convection-Diffusion	TEMPERATURE
ROM · Fluid Dynamics	Fluid Dynamics	VELOCITY_X, _Y (and _Z), PRESSURE
ROM · Potential Flow	Potential Flow	VELOCITY_POTENTIAL, AUXILIARY_VELOCITY_POTENTIAL

Each is the physics problemtype unchanged — its forms, conditions and materials produce the full-order ProjectParameters.json — plus a Reduced-order model section, a Sampling section and a Parameters list.

Not solver-verified

The manager parameters follow rom_manager.py at Kratos master (read 2026-10-14) and the driver follows Kratos' own RomManager tests, but no case was trained against a solver here. Treat the first run as a check of the generated files. The ANN-enhanced decoder (which needs TensorFlow) is not offered.

Set up a case

1. Set up the full-order case as for its physics: parts, conditions, materials, time stepping. Keep the case's VTK output on if you want the per-run results written.
2. Under Parameters, add one entry per value that varies. Varies lists every number of the case — section settings, condition values (a pressure, an imposed displacement component…) and material variables (a Young modulus, a conductivity…) — grouped as in the sidebar. Give each a minimum and a maximum.
3. Under Sampling, pick how the training and test points are drawn — Latin hypercube, Halton sequence, uniform random or a full grid — and how many. The same seed always gives the same points. A full grid takes a number of points per parameter.
4. Under Reduced-order model, choose what to train (ROM, or ROM and HROM) and test, the projection (Galerkin, LSPG or Petrov–Galerkin), the SVD truncation tolerance, the snapshot interval and the HROM settings (selection tolerance, parts whose elements or conditions are always kept).

Generate refuses a case whose parameter names no value of the case, whose minimum is not below its maximum, whose value the solver never reads, or which shares a value with another parameter. It also refuses testing an HROM that is not trained.

How a parameter reaches the solver

Generate finds where each parameter lands by generating the case twice with two probe values and comparing the documents. A Young modulus, for instance, is found in the materials file, and a pressure in the matching load process of ProjectParameters.json. The driver then writes exactly those values for each sample, so a parameter means what the form means, and a value that only changes a label is refused.

What Generate writes

File	Contents
ProjectParameters.json, the materials file, the case mesh	the full-order case, as its physics problemtype writes it
RomManagerParameters.json	the manager's general parameters, every key written explicitly from the form
RomSamples.json	the parameter names and ranges, where each lands in the documents, and the training and test points
MainKratosROM.py	the driver: builds RomManager with the case's documents, updates them per sample, then fits and tests

The driver writes kkss-rom-progress.jsonl (one line per analysis: the sample, the stage and the elapsed time) and, at the end, kkss-rom-summary-v1.json (the number of modes, the HROM counts and which stages ran). The materials file is restored after the run. Stop ends the current analysis cleanly; the summary then says the database is partial. RomManager writes its own results to rom_data/ (the basis, the singular values and the HROM element and condition ids and weights) and, with VTK output on, one Results/vtk_output_<stage><sample> folder per analysis.

Look at the results

Kratos Runs. A run of a ROM case shows a row such as ROM 12 modes · HROM 340 el / 18 cond · 9/9 runs. Its context menu has:

• Plot ROM Singular Values: the normalized singular values against the mode index, on a logarithmic axis, in the Plots workspace; how fast they fall tells how many modes the basis needs.
• Show HROM Elements: opens the case mesh and adds a selection set holding the HROM elements and conditions, so the reduced integration domain is visible on the full mesh.

MCP. case_rom returns the modes, the singular values, the HROM ids, the samples and the progress, and case_status carries a compact copy. See MCP Server.