Unlocking the engineering power of marine simulation and testing for cutting-edge ship design

About CETENA

A lot goes into building popular ships like the MSC Explora 1 or the Seven Seas Grandeur. The size and complexity of unique projects like these can be daunting. To start, you have classic naval architect topics like ship design and hull integration. Then you need to add more advanced concepts to the list like structural dynamics, vibro acoustics, overall performance issues, fuel efficiency, new propulsion methods, optimization, sea trials and certification. Managing the nuances of all this takes engineering expertise.

CETENA is a subsidiary of the Fincantieri Group and specializes in research and consultancy in the naval and maritime industry. CETENA has been involved in national and international research activities since 1962 and has carried out research and consultancy and technical assistance for shipyards, shipowners, navies and universities. CETENA has developed a partnership with Siemens Digital Industries Software and the University of Genoa to support the marine engineering ecosystem around Genoa, Italy.

CFD simulation and the marine industry

When searching for the right computational fluid dynamics (CFD) software, CETENA decided to use Simcenter™ STAR-CCM+™ software for its projects. Dr. Davide Grassi, senior naval architect at CETENA couldn’t agree more. Simcenter software is part of the Siemens Xcelerator business platform of software, hardware and services.

We use Simcenter STAR-CCM+ as our starting point when we have a new project because we need to leverage the technical support that the software offers,” says Grassi. “This was certainly the case with our ship launch project. We also use our tools from an open-source environment but we use Simcenter STAR-CCM+ as our reference software for most hydrodynamic issues.”

Several years ago, Grassi and his team tackled an overlooked issue in naval architecture simulation: full-scale vessel launching. Because the size and cost of military and commercial vessels have significantly increased, it is critical to guarantee a safe launch of the final, completed product.

“You don’t want to come across shipyards that use old launch equipment or outdated launch practices when putting these newer, bigger and taller vessels in the water,” says Grassi. “There are many areas where things could go wrong: the vessel might slide too far and hit the dock or go too deep and hit the bottom. Then there are the influences of free surface effects on structural stability or the effect of the hull’s drag resistance and waves from the vessel upon initial contact.”

CFD simulation of ship launching procedure with Simcenter STAR-CCM+.

To prevent these events, the team decided to create a physics-based digital twin of the launch vessel, slipway and launch process for Fincantieri. Throughout the development process, the team relied on using Simcenter™ Engineering and Consulting services to help refine the tool and iron out trickier aspects of the numerical model. With the comprehensive digital twin, they could check the effects of various design decisions in advance and verify the launch process, correct for potential issues and guarantee the safe operation of the vessel.

“Using the Simcenter simulation tool, we can gain valuable insight into future ship launches for our clients and analyze the effect that different design solutions will have,” says Grassi.

“Simcenter STAR-CCM+ is a high-fidelity tool. We can say this with confidence since we have compared our simulated results with actual data,” says Grassi. “We have found that the simulated results and actual data only show a 1 percent difference in accuracy. This means that we can use Simcenter to create smart simulators that can perform maneuvers with 99 percent accuracy. For this reason, we trust Simcenter STAR-CCM+ to simulate high-risk applications like vessel launches.”

Using cutting-edge research and simulation

More recently, the CETENA team and experts from the University of Genoa decided to use other aspects of Simcenter to investigate emerging ship performance issues associated with new electric propulsion systems.

Michele Martelli, a professor from the University of Genoa Naval Architecture and Marine Engineering Department, used Simcenter Amesim™ software in a thesis research project to create a dynamic model of a cruise ship in one degree-of-freedom (DOF). Using Simcenter enabled the engineering team virtually to assess and optimize mechatronic system performance to make the right choices and meet requirements already during the very early design stages. They successfully used the final Simcenter Amesim simulator as a virtual benchmark to test control logic for electric propulsion plans for difficult maneuvers like crash stops.

“We use the crash stop maneuver to prevent collisions,” says Martelli. “The ship is moving ahead at full speed and you need to stop and reverse the thrust. It’s a very challenging maneuver that could be dangerous or damaging if not properly managed by the ship’s control system.”

Using Simcenter to create a simulator for electric propulsion control logic

The best option to avoid risks is obviously to try out the vessel’s control system virtually. One of Martelli’s master’s students easily developed a reliable model of the vessel to test the electric propulsion control data using benchmark data from CETENA.

“The student had never used Simcenter before, but in a couple of months, he was able to develop a very good simulator,” says Martelli.

The student used Simcenter Amesim to create a simulator that was almost an exact match to industry experimental data, which meant it could be used to reliably test control logic on various maneuvers.

The importance of upstream simulator work

Guglielmo Sommariva, a marine engineer for CETENA, acted as an industry mentor during the thesis project. He was quick to point out the importance of using an upstream simulator to develop electrified vessels.

“The crash stop maneuver is very hard to simulate because it depends on automated parameters that are unknown early in the design process,” says Sommariva.

“Especially with new propulsion systems, this is guesswork,” says Sommariva. “It doesn’t take into consideration the control logic or other outside factors like wave or wind forces. We clearly needed a more accurate simulator upfront in the design process and created one using Simcenter Amesim. Using Simcenter Amesim and its validated libraries makes it easy for the user to change parameters quickly, try out lots of different scenarios and visualize the results in very little time.”

Using Simcenter Flomaster to perform advanced safety simulations

Andrea Gambino is a mechanical engineer and a new member of the CETENA team who is working on advanced safety simulations. Gambino and his colleagues used Simcenter Flomaster™ software for several system-level projects, including seakeeping analysis, ballistic impact analysis, shock and response spectrum analysis and one-dimensional fluid dynamic analysis.

Gambino worked on a specific project regarding cruise ship safety and used Simcenter Flomaster to evaluate the hydrodynamic pressure of the water entering the nozzles of the automatic sprinklers on board a cruise ship.

“Simulating this system is very important because these nozzles need to work properly with minimum water pressure,” says Gambino. “You need to check and evaluate that the entire system on the ship is going to work properly.”

If you don’t use simulation for projects like these, the only other possible approach is physically testing and troubleshooting the system. And this obviously isn’t very practical. Although at Fincantieri, we do perform actual onboard system testing as required by international safety standards. It is nice to know that we can use Simcenter Flomaster simulation to make sure everything will go according to plan for the real live test. ”

“Using Simcenter Flomaster helps us accurately solve tougher nonlinear issues,” says Gambino. “I have to say it’s a perfect match. If I had to create all the mathematics and an object-oriented programming approach like this, it would take me an entire year to write a decent simulation program to test the sprinklers virtually.”

Pod-propelled ship dynamic simulator in Simcenter Amesim.

The importance of sea trials

The pinnacle of thousands of hours of design, development and advanced engineering, integration and cabin design and performance simulation all comes down to the sea trial.

A sea trial is a series of mandatory tests performed at sea by the shipbuilder prior to certification and delivery to the shipowner. The main purpose is to push the vessel to its performance limits, checking top speeds, maneuverability, equipment and safety features.

A costly but mission-critical exercise

With average sea trials on a cruise ship taking about eight days, one can imagine that a sea trial carries a high but vital price tag. A sea trial operation needs to be as efficient as possible.

“Even as we are moving towards digital simulations, physical testing with models in a towing tank or the full vessel during sea trials isn’t going away,” says Matteo Codda, manager of platform engineering and research for CETENA.

“It’s the owner who wants to verify that the ship complies with the contracted performance characteristics,” says Codda. “Sea trials are not the best way to validate numerical models because the environment is not controllable or predictable. The only thing predictable about a sea trial is that it means spending a lot of money.”

Today, sea trials are used on all types of ships – from your standard sport boats to massive cruise ships and military vessels. The crew familiarizes themselves with the ship, which can take hours or weeks (even months for certain types of military ships) and confirms everything from basic seaworthiness and maneuverability to performance metrics like fuel efficiency, emissions, noise and vibration limitations, maximum speeds and various safety features.

An average sea trial on a cruise ship takes about 8 days.

A testing center for excellence

One of the testing and sea trial experts for CETENA is Federico Gaggero, who has used Simcenter Testlab™ software and Simcenter SCADAS™ hardware since 2005.

The CETENA testing team continues to use Simcenter software and hardware for various testing scenarios ranging from acceleration measurements during shock tests to sea trial data acquisition and onboard acoustic testing. They are especially fond of the Siemens token system, which offers full flexibility for using the software for different applications.

“This token system allows us to use Simcenter Testlab to turn certain models off and on,” says Gaggero. “It gives us incredible flexibility when using Simcenter testing systems. We can increase the number of tests and offer our clients various tests.

“99 percent of our work is performed with some of our Simcenter testing tools. We can trust the results. We have very good support from Simcenter experts from the Torino office as well as online help,” says Gaggero.

“It does happen that we need some guidance during a test and the Simcenter technical support team is always there to help solve the problems so we can continue the test – even when we are at sea on a sea trial or completing a real challenging test request for a customer. This is much better than turning the boat around, going back to port and starting over or saying that we can’t do it. The entire Simcenter testing solution and technical support team is just excellent.”

Using simulated performance indicators to drive success

Everything on the simulation and testing side was correlated so that the final sea trial was successful.

“Sometimes we use simulation to extrapolate sea trial results because the ship is still under construction or is not complete,” says Codda. “These are performance indicators that show how the vessel should perform during a maneuver like the crash stop test.

We look at everything in the finest detail from supplier requirements for materials installed on board to final systems performance according to vessel certification, shipowner requirements
and military standards.”

The CETENA team believed that it was important to validate their simulation and numerical models with experimental measurements and testing. In the marine industry, it is quite unusual for simulation and test experts to work closely in the same company. Codda and team felt fortunate to be able to collaborate since they work in the research center for Fincantieri. This gives them direct access to the ships, the test data and the validated simulations.

“I’m convinced that multidisciplinary simulation and an accurate digital twin will be the future,” says Codda. “We are constantly building more complex vessels that require more advanced simulation scenarios. And when we start to integrate and interoperate different simulations, it will be very beneficial to remain in the same simulation and testing solution portfolio.”

He concludes, “Of course, how to integrate all these different simulation disciplines is one of the key points on my mind as well as the experimental testing and validation process. We will
need more feedback from the field to make sure that our models are correct. In general, simulation and CAE is comparatively right. A designer can see if one decision is better than
another, but it is another matter to have this information quantitatively.”