Computational Fluid Dynamics · OpenFOAM Specialist · Copenhagen

Precision CFD for
the green transition

STROMNING develops novel CFD models, custom OpenFOAM software, and provides specialist consulting — with a particular focus on floating wind, maritime, and free surface flow applications.

Get in touch See projects
20+ Peer-reviewed publications
isoAdvector Original author
FloatStepper Original author
DTU · DHI · Stiesdal · Siemens Gamesa · Ørsted Past collaborators

Client endorsement

“STROMNING supported us with advanced CFD simulations of our heave plate design. The study combined deep hydrodynamic expertise with a structured and methodical approach. The results strengthened our technical confidence and supported critical design evaluations. Communication was clear and proactive, and all milestones were met as agreed.”

Stiesdal Offshore

Floating offshore wind · Denmark

What I do

Specialist CFD services

From novel numerical method development to production OpenFOAM software and hands-on consulting — for projects where simulation accuracy is non-negotiable.

01

CFD Model Development

Development of bespoke computational fluid dynamics models tailored to specific flow problems. Includes novel numerical methods, experimental validation, and full documentation. Particularly specialised in interfacial and free surface flows.

Free surface flows Interfacial dynamics FSI Validation Floating wind

02

Custom OpenFOAM Software

Custom solvers, libraries, and tooling built on the OpenFOAM framework. Code that integrates cleanly with existing workflows, with training and handover included. Author of isoAdvector and FloatStepper — both widely used in the OpenFOAM community.

Solver development Custom libraries OpenFOAM isoAdvector FloatStepper

03

Specialist Consulting

Expert input on CFD strategy, simulation methodology, and technical problem-solving for industrial and research projects. Available for embedded collaboration or independent technical review.

Technical review Methodology Floating wind Maritime Offshore renewables

04

R&D Partnerships

Collaboration on funded research projects — from initial consortium formation and proposal writing through to project execution. STROMNING can join as a technical partner co-defining the research agenda, or fill a targeted CFD expertise gap in an existing consortium. Experience with national and EU funding programmes, including as a named partner in FloatStep and FloatLab.

Consortium building Proposal writing EU funding National programmes Floating wind

05

OpenFOAM Code Porting & Upgrades

Many organisations carry in-house OpenFOAM code that has fallen behind current releases — breaking with API changes, new mesh handling, or updated numerics. STROMNING can audit, port, and modernise custom solvers and libraries to the latest OpenFOAM version, restoring compatibility while preserving the functionality your team depends on.

Code porting API migration OpenFOAM Legacy solvers Code audit

06

OpenFOAM Training

Hands-on training for engineers and researchers — from OpenFOAM fundamentals to advanced topics in marine hydrodynamics and multiphase flows. Courses can be tailored to your team's level and use cases, covering solver setup, meshing workflows, post-processing, and custom development best practices.

Fundamentals Multiphase flows Marine hydrodynamics Floating wind isoAdvector

Open-source software

Novel methods, freely available

Two original CFD algorithms developed at STROMNING — both peer-reviewed, open-source, and adopted across the OpenFOAM ecosystem.

isoAdvector

Geometric Volume-of-Fluid · OpenFOAM

A geometric VOF method for accurate and efficient advection of a fluid interface on arbitrary meshes in OpenFOAM. isoAdvector reconstructs the interface as an isosurface of the indicator function and computes face-fluxes geometrically — delivering sharper interfaces and better mass conservation than algebraic VOF methods. Now part of the standard OpenFOAM distribution.

GitHub ↗ Key paper ↗

FloatStepper

Floating body FSI · OpenFOAM

A novel time integration scheme for strongly coupled fluid–structure interaction in OpenFOAM. FloatStepper treats the motion of floating bodies and the surrounding fluid in a tightly coupled manner, eliminating the added-mass instability that plagues conventional partitioned FSI solvers — without requiring iteration. Designed for floating wind and naval applications.

GitHub ↗ Key paper ↗

Selected projects

R&D projects

A selection of research and industrial projects spanning floating wind, wave–structure interaction, and advanced multiphase flows.

Floating wind · FloatStep · Innovation Fund Denmark

FloatStep — floater design and hydrodynamic modelling

Four-year Danish R&D project developing improved calculation models and designs for floating offshore wind foundations. STROMNING contributed CFD methods for flow calculations around floaters. Partners include DTU, DHI, Siemens Gamesa, Stiesdal Offshore, and the University of Western Australia. Funded by Innovation Fund Denmark (DKK 15.8M).

Project news ↗

Floating wind · FloatLab · Innovation Fund Denmark

FloatLab — test laboratory for next-generation floating wind

Consortium project establishing a combined physical and digital test laboratory for floating wind turbines in the 20 MW class. Focused on uncovering new physics: 3D wave dynamics, breaking wave loads, turbulence, mooring failures, and coupled hydrodynamic–aerodynamic–control behaviour. STROMNING provides CFD software. Partners: DTU, DHI, Siemens Gamesa, Stiesdal Offshore, Ørsted. Funded by Innovation Fund Denmark (DKK 22.3M total).

Project news ↗

Coastal & marine CFD · Deltares · Roskilde University

isoAdvector in porous media — coastal and offshore structures

Extending the isoAdvector geometric VOF method to free-surface flows through porous structures such as breakwaters and rubble-mound foundations. Initial development was sponsored by Deltares; the work was later matured and validated together with Konstantinos Missios at Roskilde University, culminating in a peer-reviewed paper and integration into the official interIsoFoam solver shipped with OpenFOAM since v2112.

Paper ↗

Two-phase flow · DLR German Aerospace Center

TwoPhaseFlow — open-source multiphase CFD framework

Collaboration with Henning Scheufler at DLR on an open-source OpenFOAM framework for two-phase flow solver development. Adds surface tension and phase change modelling capabilities — including the height function and parabolic fit methods for interface curvature — along with validation benchmarks and adaptive mesh refinement. Published in the OpenFOAM® Journal.

GitHub ↗ Paper ↗
Johan Roenby

About

Johan Roenby

Founder · Computational mathematician & fluid dynamicist

STROMNING is Johan Roenby — a specialist in computational fluid dynamics with a focus on interfacial and free surface flows, floating body dynamics, and the numerical methods that underpin them.

Johan is the originator of isoAdvector, a geometric Volume-of-Fluid method now part of the standard OpenFOAM distribution and used worldwide for free surface flow simulation. He is also the author of FloatStepper, a novel FSI time integration scheme that eliminates the added-mass instability in floating body simulations — with direct application to floating wind turbine design.

With a PhD in applied mathematics and more than a decade of research and industrial consulting, Johan brings a level of specialist depth that generalist CFD firms cannot match. Past collaborators include DTU, DHI, Stiesdal Offshore, Siemens Gamesa and Ørsted.

Google Scholar ↗ GitHub / isoAdvector ↗ GitHub / FloatStepper ↗ LinkedIn ↗

Research

Selected publications

Peer-reviewed work underlying STROMNING's methods. Full list on Google Scholar.

2025

Directional focused wave group response of a floating wind turbine: Harmonic separation in experiments and CFD

Renewable Energy

DOI ↗
2024

A robust algorithm for computational floating body dynamics

Royal Society Open Science

DOI ↗
2023

TwoPhaseFlow: A framework for developing two-phase flow solvers in OpenFOAM

OpenFOAM® Journal

DOI ↗
2023

Extending the isoAdvector geometric VOF method to flows in porous media

OpenFOAM® Journal

DOI ↗
2022

A comparative study of two open-source state-of-the-art geometric VOF methods

Computers & Fluids

DOI ↗
2020

Validation of volume-of-fluid OpenFOAM® isoAdvector solvers using single bubble benchmarks

Computers & Fluids

DOI ↗
2019

Accurate and efficient surface reconstruction from volume fraction data on general meshes

Journal of Computational Physics

DOI ↗
2016

A computational method for sharp interface advection (isoAdvector)

Royal Society Open Science

DOI ↗
View all publications on Google Scholar →

Contact

Tell me about your project

Whether you have a well-defined problem or are still scoping — happy to discuss how STROMNING can help.

Email
Phone +45 29 93 19 23
Based Luftmarinegade 62, 1432 Copenhagen, Denmark
CVR DK39319616