In order to save fuel, international regulations require ships to become significantly more efficient in the future. With the help of cutting-edge flow simulation software, Siemens is helping manufacturers of ship technology to significantly enhance efficiency.
by Tim Schröder
Many people associate summer cruises with sunshine, blue skies, and a bracing ocean breeze. But they often forget that the approximately 70,000 commercial and cruise ships that are in use today consume heavy fuel oil, thus making a major contribution to air pollution all over the world. Moreover, many of the ships operating today are not especially efficient and need comparatively large amounts of this dirty fuel. In line with current regulations, the London-based International Maritime Organization is therefore requiring that new ships built from 2025 on must be at least 30 percent more efficient than those built until 2014.
New ships built from 2025 on must be at least 30 percent more efficient than those built until 2014.
How can ships’ fuel consumption be reduced by almost a third within just a few years? Norbert Bulten knows the answer. “A crucial role is played by the design of the ship, especially that of the propulsion system, the propeller, the transmission, and the flow of water around the rudder and propeller,” he says. Bulten is the Product Performance Manager Propulsion of ship technology manufacturer Wärtsilä in Drunen in the Netherlands and has been working to optimize propulsion designs for the past 20 years. From the very start, he has focused on computer support – and on software from Siemens that enables him to conduct flow calculations. Such calculations are known as computational fluid dynamics, or CFD. In simple terms, CFD makes it possible to determine whether a ship’s propulsion system ensures an optimal flow of water around the hull, whether there are forces of resistance, and how efficiently the engines’ power is transformed into thrust. At Wärtsilä, the software platform that is used today for CFD is Siemens Simcenter STAR-CCM+.
Only 20 years ago, shipping companies had little faith in CFD, says Bulten. “For decades, companies in our sector have trusted tests conducted in a flow channel. In this process, ship models are pulled through water. This is how they test how well a ship design functions.” Initially, Bulten and his team only calculated the data for individual components, such as the propeller and its immediate surroundings. However, he was able to demonstrate again and again that CFD can make a big contribution to the testing process. For example, it has helped to improve a ship under construction that showed increased flow resistance. By means of CFD, the design was minimally adjusted, and the ship was correspondingly re-welded while she was still in dry dock. After a few days of work, the ship was perfect. “All the same, the companies still had reservations for a long time,” says Bulten. However, he adds, the situation is rapidly changing today. For quite a while now, CFD has been used to design ships from start to finish – in true-to-life dimensions. “A computer reproduces the behavior of an actual big ship moving through water. That gives us a comprehensive overview of the flow characteristics.” The design of the ship’s propeller plays a key role. “In contrast to auto production, every ship is unique, and an optimally adapted propeller must be developed especially for it. Designing this propeller is an art.” As usual, propeller designs are created with the help of CAD programs on Siemens’ NX platform. After that, a computer uses CFD to tease the last little bit of efficiency into the design.
This individualized calculation procedure is also of interest for the retrofitting of ships. As a result of the economic crisis of 2008, the shipping sector shifted to slower rates of speed for its big container ships in order to save fuel. Their speed was reduced from the previous 28 knots to 20 knots. However, at lower speeds traditional propellers, which have six blades and a large surface area, are less efficient. “We were able to persuade ship operators to use new narrow propellers with four blades and a small surface area, and we used CFD to adapt a suitable propeller to each individual ship. As a result of this retrofitting, shipbuilders will be able to save lots of fuel over the years,” Bulten says.
“Testing in a water tank will probably be replaced more and more by calculations in a computer."
Bulten has scored a number of successes in recent years, thanks to his ability to calculate the efficiency of ships in true-to-life dimensions. One of his clients recently ordered a ship that would travel at a speed of over 13 knots. Model tests in a flow channel predicted that the initial design would not enable the ship to reach this speed. However, the CFD program run on Simcenter STAR-CCM+ said the ship would manage 13 knots, and the client decided to build the ship according to the initial design. Bulten was proved right. In a test voyage at the beginning of 2018, the ship easily reached a speed of 13 knots. “That definitively showed us and many sector experts that today CFD is at least as effective as tests in a tank of water,” says Bulten.
In spite of all the advantages, CFD and water tank tests still have one thing in common: Ships are still tested under real-life conditions. Indeed, both are carried out at cruising speed in calm water. In view of this, Bulten now wants to make CFD calculations more dynamic. “In the future we want to feed the CFD program with authentic measurement data from the real-life operation of ships at sea, including propeller operation, turbulence, and the influence of waves,” he says. “For this purpose, a digital twin of a future ship will be created in the CFD program and tested on a computer under quasi-real conditions in order to optimize the efficiency of the design.” In view of such developments, Bulten believes that CFD is today at the beginning of a new era. “Testing in a water tank will probably be replaced more and more by calculations in a computer,” he says.
Picture credits: Wärtsilä Propulsion
Stay up to date at all times: everything you need to know about electrification, automation, and digitalization.
It looks like you are using a browser that is not fully supported. Please note that there might be constraints on site display and usability. For the best experience we suggest that you download the newest version of a supported browser: