Developments in CFD technology offer big gains in hullform design and provide near-perfect real-world sea-state simulations
Computational fluid dynamics (CFD) is not a new technology, but every wave of technological improvement helps push its capabilities that bit further. CFD offers a virtual representation of fluid flow for advanced analytics in the latter design phases of vessels, machinery and fluid-handling systems, helping improve hullforms and thus a vessel’s ability to efficiently flow through water.
CFD enables naval architects to perfect hull shapes, optimising them for the speed and performance of a respective vessel. In such projects, CFD is viewed as a software alternative to model tank studies.
This advanced technology can also be used for the design of propellers, to ensure that the flow of water is optimised and maximise thrust forces from propulsion. It can be used to design propeller blades and turbomachinery which require precise engineering.
For marine turbochargers, CFD is used to maximise air flow and therefore engine power. It can also be used for simulating single fluid or multiphase flow through pipeworks and pumps.
In the dredging sector, CFD is used to model complex multiphase pumping, helping to analyse flow through nozzles and the interaction of equipment with sediments. In the offshore and passenger shipping sector it is used to simulate air flow over marine infrastructure, helping reduce the impact of inclement weather, or increase energy generation from wind turbines.
“Once the simulation is built, the workflow can be automated to test the model in a variety of realistic sea-states, or through self-propelled manoeuvres”
Tug designer Robert Allan has used CFD in producing its latest tug, pilot vessel and fireboat designs, optimising hullforms for resistance, stability and trim, while minimising tank-based model testing. “We trust the CFD more than we trust model tests,” said president and chief executive Mike Fitzpatrick. “It is good for finding solutions to problems in motion and stabilisation and it pushes the boundaries of what is possible,” he added.
CFD software is used byRobert Allan to optimise the design of vessel hulls and propulsion systems
Robert Allan uses CFD to analyse different propulsion systems on tugs, and Mr Fitzpatrick explained the technology allowed the company to model Voith drives in CFD and conduct finite element modelling to optimise vessel structures. Finite element modelling is the analysis of a finite number of small elements in a structure, such as a ship’s hull, propeller blade or machinery component. It allows designers to visualise stress or fluid flow on these segments and then create a larger 3D model containing the findings, which is adjusted and analysed over numerous cycles.
One of the major providers of CFD technology, Numeca International, has enhanced its marine CFD portfolio following the acquisition of Swiss software company, Flowkit.
The acquisition gives Numeca’s CFD software additional multiphysics applications, helping in the analysis, design and optimisation of turbomachinery, marine, aeronautics, aerospace and energy systems.
FlowKit had developed advanced mathematical coding to help solve complex equations originating from CFD program applications. This is mainly used by Numeca’s OMNIS platform for external aerodynamics applications, such as offshore wind turbines.
In August this year, Numeca released version 2.2 of OMNIS, which features its Hexpress automated mesh generator program. This allows meshes to be used for finite element CFD modelling of structures, such as ship hulls and propulsion blades.
As part of the OMNIS update, Numeca added an open source version for drag analysis, separate phase fluid predictions and gas modelling. It also included advanced mesh optimisation options for finite element analysis of different mesh models.
In July the company also updated its main blade and turbomachinery analysis software. The release of Fine/Turbo 13.1 improves the method for quantifying turbulence in fluid flow around blades. This includes specifying turbulence conditions at the boundary of the fluid and solid element.
It also enables engineers to analyse convenient quantities, such as the intensity, viscosity ratio and the hydraulic diameter of the turbulence. Fine/Turbo can now be used on computers with multicore processing units for faster calculations.
Fine/Marine also saw its ability to simulate mono-fluid and multi-fluid flows around different types of ship improved. The CFD software can be used to analyse vessel types including merchant ships, workboats, tugs and yachts. Naval architects use the program to simulate appendages on hulls, to optimise hullforms and streamline propulsion arrangements.
Elsewhere, Siemens’ Star-CCM+ programme enables full-scale CFD vessel simulations under real operating conditions, enabling naval architects to improve the design of hulls and superstructures. It features an automated set-up and post-processing tool for ship resistance and dynamic trim calculations.
Designers can predict vessel resistance at full or model scale, including dynamic changes in trim. Once the simulation is built, the workflow can be automated to test the model in a variety of realistic sea-states, or through self-propelled manoeuvres.
Siemens said Star-CCM+ allows designers to model propulsion systems, including the interaction between rotating propellers and the flow around the hull. It helps predict the onset and influence of cavitation, which impacts performance, to help improve propeller design.
Siemens Star-CCM+ program offers these types of analysis for marine applications
The overset mesh technology within with Star-CCM+ facilities the analysis of vessel stability and performance under realistic and extreme sea conditions. This includes slamming and sloshing simulations at full scale. It also removes the need to apply scaling approximations to produce more accurate loads for structural analyses, noted the company.
In August, Engys released version 3.1.0 of its Helyx CFD software, which includes further applications for the add-on module, Helyx-Marine. New features support more advanced meshing algorithms, multiphase flow solutions, improved handling of fluid-solid boundary conditions and more shape optimisation tools.
Helyx-Marine has a new captive manoeuvring simulation, allowing hydrodynamic optimisation of ship hullforms and propulsion systems, verification of hull performance and analysis of offshore structures.
The company said this module also features a set of transient solutions for simulating floating bodies and seakeeping conditions in forward motion. It uses surge motion to simulate various seakeeping conditions, dynamic trim and stability.
Orca’s 3D Marine program has been combined with Simerics multipurpose CFD software. This offers desktop analysis tools for designers, so they do not need to become specialised CFD experts. Orca3D Marine CFD enables the analysis of multi-hulled vessels with appendages, compute water and air streamlines, analyse longitudinal dynamic stability and wave-hull interaction. It can analyse vessel heaves, pitching and trim, while benchmarking vessel performance against full-scale data, model tests and other analysis codes.
TotalSim’s CFD program was developed for Formula 1 racing but can be used to simulate the performance of high-speed power boats, yachts, leisure craft, tankers, ferries, cargo ships and offshore drilling rigs. It enables the optimisation of hullforms, submerged appendages, propellers and other submerged structures. TotalSim can provide detailed aerodynamic analysis of any surfaces above the waterline.