# FreSCo+ - The Free-Surface Code

The project aims to develop a viscous hydrodynamic simulation tool which features both industrial applicability (i.e. robustness and process compliance) and accuracy. The development is jointly performed by TUHH (M-8), the Hamburg Ship Model Bassin (HSVA) and the Dutch Maritime Research Institute (MARIN). The result of the joint effort is the** Finite-Volume Navier-Stokes **procedure **FreSCo**. The FreSCo^{+} software is an enhanced capabilities spin-off of FreSCo.

CFD-Modelling of Maritime Applications using FreSCo+

- Manoeuvring & Seakeeping
- Ship Dynamics
- Sloshing & Free-Surface Flows
- Propeller Flow Simulations
- Steady Wave Resistance
- Cavitation Modelling
- Cavitation Analysis

#### Computational Procedure

The segregated algorithm is based on the strong conservation form of the momentum equations and employs a cell-centred, co-located storage arrangement for all transport properties. The procedure can be used in conjunction with structured-grid and unstructured-grid discretisations, based on arbitrary polyhedral cells or hanging nodes.

The implicit numerical approximation is second-order accurate in space and time. Integrals are approximated using the conventional mid-point rule. Diffusion terms are subsequently approximated using second-order central differences, whereas advective fluxes are approximated using high-order bounded (monotonic) schemes. The latter are applied in scalar form by means of a deferred-correction approach.

The odd-even decoupling problem of the cell-centred scheme is suppressed with a fourth-order artificial dissipation pressure term in the continuity equation. The solution is iterated to convergence using a SIMPLE-type pressure-correction scheme. The data structure and numerical approximation supports mass-conservative overset-grid technologies based upon a close coupling of the employed grids using fast Delauny tessellation approaches.

Various turbulence-closure models are available with respect to statistical (RANS) or scale-resolving (LES, DES) approaches. Two-phase flows are addressed by interface-capturing methods based upon the Level-Set or Volume-of-Fluid (VOF) technique. Specific interface sharpening techniques in line with a conservative interpolation for face-based pressures are available for two-phase flow simulations. In order to simulate cavitating flows, the VOF-method can be combined with a selection of mass-transfer models. Optionally, more accurate Lagrangian bubble-techniques can be used to determine the vapor content.

The software also supports the solution of the segregated, pressure-based adjoint system in order to determine a continuous sensitivity distribution ready to be eomployed in an optimisation strategy.

Linear equation systems are solved by means of Krylov-subspace methods offered by the PETSc library. Since the data structure is generally unstructured, suitable pre-conditioned iterative sparse-matrix solvers for symmetric and non-symmetric systems (e.g. GMRES, BiCG, QMR, CGS or BiCGStab) can be employed. The algorithm is parallelised using a domain-decomposition technique based on a Single Program Multiple Data (SPMD) message-passing model, i.e. each process runs the same program on its own subset of data. Inter-processor communication employs the MPI communications protocol. Load balancing is achieved using the ParMETIS partitioning software.

#### Personnel

Prof. Dr.-Ing. Thomas Rung

Dipl.-Ing. Thierry Maquil

M.Sc. Bahaddin Cankurt

Dr. Sergey Yakubov

Dipl.-Ing. Jörn Kröger

M.Sc. Farhan Matin

Dipl.-Technomath. Xiaojing Luo

MSc. Mehrdad Javanian

Dipl.-Ing. Patrick Schiller

M.Sc. Svenja Völkner

Dipl.-Ing. Wibke Wriggers

#### Funding

The software is also used for BMWi-MARTEC project* PROPSEAS* (*PROSEE*), the BMWi-project FORM-PRO, the European FP7 projects STREAMLINE & TARGETS and the BMWi projects KONKAV 1, 2 and TUG Design.

up-to-date: 2009-09-30