CFD – Virtual Towing Tank
Virtual Towing Tank – a three-year project
Damen is now two years into a three-year project investigating Computational Fluid Dynamics (CFD) tools and the contribution they can make to accelerating the ship design process, while at the same time cutting the associated costs and improving the quality of products in the group’s portfolio.
The project belongs to the wider corporate programme Damen Cooperative Research (DCR); a cross group programme focusing on the strategic technologies that Damen will need in the years ahead to gain advantage and stay competitive in the market.
Figure 1: As real simulation of the Lloyd’s test case General Cargo “Regal” showing the propeller swirling flow structures and their interaction with the rudder.
CFD has been identified as one of those, since it has the potential to change the rules of how vessel design and development is conducted by combining applied mathematics, physics and High Performing Computing platforms (HPC) to visualise in a simulated 3D environment how individual vessels will behave in a wide range of wind and wave conditions. Once validated, CFD tools can be used to replace the expensive and time-consuming process of building precise scale models and then assessing their performance in towing tanks and wind tunnels. For this reason, the overall project has been named the ‘Virtual Towing Tank’ (VTT).
There is a wide range of commercial CFD software packages available in the market. These are available for the various industries involved in transportation of all types as well as defence, architecture, power generation and medicine. The VTT project has been investing in the verification, validation and implementation of a range of CFD tools, both commercial and open source, to determine the margins of accuracy available and the reliability of the answers that can be gained.
At the start of the project it was important to decide where resources should be focused. The various participants were polled as to their priorities, and the areas of interest to a majority of those involved included seakeeping, manoeuvring, resistance in waves and powering. These in turn were condensed into three major research areas; calm water resistance, added resistance in waves and ship propulsion. These activities form the core of the VTT project.
Figure 2: Flow streamlines and computational mesh used for the analysis of the ASD Tug 3212
CFD is already used by a number of companies across the Damen group, including Damen Shipyards Gorinchem and Damen Schelde Naval Shipbuilding, together with naval architects Knud E. Hansen and manoeuvring specialists Van der Velden Marine Systems. Applications include the conceptual studies of new designs, detailed product development, research and troubleshooting. One of the main objective of the VTT project therefore has been to bring these different pools of expertise together to jointly develop a comprehensive body of knowledge on the use and validity of CFD tools and their applicability within the Damen Group.
External partners both from research institutes and academia, such as MARIN (Dutch Maritime Research Institute) and TU Delft (Delft University of Technology), are also closely involved in the process.
In order to facilitate the task, it has therefore been necessary to build a platform that could work as a shared workspace. Within it Damen teams and external partners can connect with each other globally to collaborate on projects, share knowledge and perform advanced simulations.
Unsteady hydrodynamic pressure contour plot on the bottom of a Tug sailing under a drift angle, showing the behavior of the separated flow region.
The power of the Cloud
Since the start of the project, the shared computational platform has been transformational. Today, the right choice of a Cloud-based HPC platform allows Damen CFD engineers, wherever in the world they may be, to share not only unlimited computing power but also the workspaces in which they operate, thereby ensuring real-time collaboration. This removes the need for the exchange of data files in order to update colleagues with the last versions of designs. With everyone working in the same virtual space on the same projects, the ability to share knowledge and ideas in real time delivers a sense of common purpose and achievement that ensures energy and impetus among the participants.
Figure 3: Magnified Cloud Value
Even at this early stage we are seeing results as individual elements of Damen’s overall CFD programme start to deliver useful data that can be fed into the design and optimisation process. Damen customers are already benefiting from shorter delivery times and more efficient ship designs.
CFD is also demonstrating its value in identifying and addressing design and performance issues that otherwise might not have been evident until much later in the design and build of a vessel. As such, it can help avoid expensive modifications having to be made at some point in the future. Savings like these are hard to quantify, but there is no denying that in these circumstances the VTT programme has proved that CFD can deliver real added value in the early design phases, particularly where non-standard vessels are involved. This conclusion is supported by the numbers themselves: in 2017, 70% of all CFD work was in direct support of commercial projects, spread right across the group. The remaining 30% was targeted research in support of Damen’s conceptual product development and R&D programmes, laying the basis for a competitive and productive future.
Figure 4: Monitored cloud usage statistics in 2017