MODEL THE COMPLEXITY
A decades-long partnership in marine simulation and testing innovation
By Jenn Schlegel
CETENA, Simcenter and the University of Genoa join forces to create a marine engineering ecosystem to meet current industry challenges.
Unlike the automotive industry or even aviation, the marine industry, for the most part, faces an extreme challenge when it comes to manufacturing: every ship is unique. Although segments of the industry -- such as “smaller” luxury yachts and various sport boat segments -- do production-line type of assembly, for the most part, big players like Fincantieri, the largest cruise ship builder in the world, make bespoke or practically bespoke vessels*. The product line includes everything from aircraft carriers and military frigates to mega-yachts and ultra-luxury cruise ships that resemble small villages.
It is probably a huge understatement to say that from an engineering standpoint, there are a lot of angles to cover when building a ship like the MSC Explora 1 or Seven Seas Grandeur. Just the size and complexity of projects like these can be mind-boggling from an outsider’s perspective. Of course, you have classic naval architect topics like ship design and hull integration, which people might argue is the easy part these days. And then you have the more advanced topics like structural dynamics, vibro-acoustics, overall performance issues, fuel efficiency and new propulsion methods, optimization, and sea trials and certification. This is where the real engineering expertize takes center stage. And thanks to a strong partnership between CETENA, Siemens and the University of Genoa, the marine engineering ecosystem around Genoa, Italy is certainly thriving.
CFD simulation and the marine industry
Ask anyone for the reference CFD software in the marine industry and there is a good shot that the response will be Simcenter™ STAR-CCM+™ software. This is pretty much the case as well for Dr. Davide Grassi, Senior Naval Architect at CETENA.
“Although we tend to use Simcenter STAR-CCM+ as our reference software for most hydro-dynamic issues, we also use our own tools and tools from open-source environments.” He adds, “Simcenter STAR-CCM+ is our starting point when we have a new project because we need to leverage the technical support that the software offers. This was certainly the case with our ship launch project.”
Several years ago, Dr. Grassi and his team tackled an “overlooked” issue in naval architecture simulation: full-scale vessel launching. Especially since the size and cost of both military and commercial vessels have dramatically increased, guaranteeing a safe launch of the final, completed product has become mission critical.
“What you don’t want happening is that shipyards use old launch equipment or outdated launch practices when putting these new bigger and taller vessels in the water. There are all types of 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 first contact,” explains Grassi.
To prevent these events, the team decided to create a full physics-based digital twin of the actual launch vessel, slipway and launch process for Fincantieri. Throughout the development process, the team counted on 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 well in advance and verify the launch process, correct for potential issues and guarantee the safety of the vessel upon launch.
“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.
Concludes Grassi, “Simcenter STAR-CCM+ is a high-fidelity tool. And we can say this with confidence since have had the chance to compare our simulated results with actual data. We have found a very minor difference of 1%. We trust this solution based on Simcenter STAR-CCM+ to simulate very risky applications, like vessel launches.”
Cutting-edge research and a simulator for the Italian marine industry ecosystem
More recently, the CETENA team has turned to other parts of the Simcenter advanced engineering portfolio to solve common marine engineering issues. A recent research project is a true example of the strength the Italian marine industry ecosystem and the growing partnership between the University of Genova, Siemens and CETENA.
The project was to create a dynamic model or simulator of a cruise ship in one degree of freedom in Simcenter Amesim. The final Simcenter Amesim simulator would be used as a virtual benchmark to test control logic for electric propulsion plans for difficult maneuvers like crash stops.
“The crash stop maneuver is used to prevent collisions. The ship is going 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,” explains Martelli.
A Simcenter simulator for electric propulsion control logic
The best option to avoid risks is obviously to try out the control system on the vessel virtually. For his thesis project, one of Prof. Martelli’s masters students, who had never used Simcenter™ Amesim™ software before, developed a reliable model of the vessel to test the electric propulsion control data using benchmark data from CETENA.
“Just to let you know, he had never opened the software previously. And within a couple of months, he was able to develop a simulator. A very good one,” adds Martelli.
The Simcenter Amesim simulator was almost an exact match to industry experimental data, which meant that it could be reliably used to test control logic on a variety of maneuvers.
“When we started to test various control logic options during maneuvers on the Simcenter Amesim simulator, I was happy with the results,” explains Martelli. “The software was quite intuitive to use – especially if you have a good background in simulation and are willing to learn new stuff.”
The importance of upstream simulator work
Guglielmo Sommariva, a marine engineer at CETENA and thesis project supervisor, acted as an industry mentor during the thesis project. He was quick to point out the importance of upstream simulator work in the overall development of electrified vessels.
“The crash stop maneuver is very hard to simulate because it depends on automated parameters that are not known early in the design process. In most cases, designers don’t have a clear idea about the automation plan. Often, they make a prediction using basic information like correlating the ship’s mass, the velocity, the propulsion plans and the time necessary to stop the ship completely.”
“Especially with new propulsion systems, this is guesswork; 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 we were able to create one in Simcenter Amesim,” states Sommariva. “And it helped that Simcenter Amesim, with 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.”
Advanced safety simulations with Simcenter Flomaster
One of the newer members of the team who is working on some of those advanced and complicated simulations is Andrea Gambino, a Mechanical Engineer at CETENA. Gambino and his colleagues have worked on a variety of simulation projects including sea-keeping analysis, ballistic impact analysis, shock and response spectrum analysis, and one-dimensional fluid dynamic analysis, where he used Simcenter Flomaster for several system-level simulation projects.
One project involved an important aspect of cruise ship safety, a topic close to the heart of all at CETENA. Gambino used Simcenter™ Flomaster™ software 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. So you need to check and evaluate that the entire system on the ship is going to work properly.“ explains Gambino. “After this first project, we used our simulation model together with the engineers at Fincantieri to model the complete onboard firefighting system.”
He is quick to point out the obvious advantages of simulating fire sprinkler systems.
“If you don’t use simulation for projects like these, the only other possible approach is physically testing and troubleshooting the system. 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 with the Simcenter Flomaster simulation, everything will go according to plan for the real live test.”
“Simcenter Flomaster matches very well with common theoretical formulas related to one-dimensional dynamics and it solves accurately non-linear issues. I have to say it is a perfect match.” He adds, “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.”
Sea trials: A costly but mission-critical exercise
And speaking of real live tests, the pinnacle of thousands of hours of design, development and advanced engineering, integration and cabin design and performance simulation – all comes down the sea trial.
For those unfamiliar with term, a sea trial is a series of mandatory performance and safety tests performed at sea by the shipbuilder prior to certification and delivery to the shipowner. Naval insiders like to call it a shakedown cruise because the main purpose is to push the vessel to its performance limits. Depending on sea conditions, this can cause quite a bit of vibrations on board. At times, fittings and fixtures loosen and “shakedown”.
A sea trial can be as simple as taking a small luxury speed boat out with an NVH expert, a laptop running Simcenter™ Testlab™ software hooked up to trusty and tough Simcenter™ SCADAS™ data acquisition hardware and experienced captain for those tricky maneuver’s. A few hours on the high seas and you’ll have the job done. On the other side of the spectrum, a sea trial on a mega-cruise ship like the MSC Explora or Seven Seas Grandeur can take about a week, running the cruise ship over 2500 kilometers and take a full crew and testing staff of 500 people to complete.
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 more and more towards digital simulations, physical testing with models in a towing tank or the full vessel during sea trials aren’t going away,” explains Codda.
“You must remember that sea trials are more, let's say, contractually related. So it's the owner who wants to see and touch and verify that the ship complies with the contracted performance characteristics. Sea trials are not the best way to validate numerical models because the environment is not controllable, it is not predictable." He quips, “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. Taking hours or weeks (even months for certain types of military ships), the crew familiarizes itself with the ship and confirms everything from basic seaworthiness and maneuverability to performance metrics like fuel efficiency, emissions, noise and vibration limitations, maximum speeds and a variety of safety features.
A testing center of excellence
One of the experts at CETENA involved in testing is Federico Gaggero, a long-time Simcenter Testlab and Simcenter SCADAS user. Their main test center is located right in Fincantieri’s Riva Trigoso shipyard, slightly south of Genoa. It is one of the company’s most important test centers specializing in military and civil certification and shock testing. It is the unique location in Europe for MIL S 901 D shock certification, which is required for most shipboard machinery, equipment, systems, and structures. The test center is equipped with a NavSea-accredited medium-weight shock machine, one of two in Europe.
The testing team at CETENA has used Simcenter testing solutions since 2005 and the team continues to use the software and hardware for a variety of testing scenarios ranging from acceleration measurements during shock tests, to sea trial data acquisition to onboard acoustic testing. They are especially fond of the Siemens token system, which offers full flexibility when it comes to using the software for different applications.
“This token system lets us turn off and turn on certain modules in Simcenter Testlab. It gives us incredible flexibility when using our Simcenter testing systems. We can increase the number of tests and offer our clients a wider range of tests.”
“99% of our work is performed with just a couple 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 Federico 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.”
Simulated performance indicators spell success
Matteo Codda is quick to point out that everything on both the simulation and testing sides is correlated so that the final sea trial is success.
“Sometimes simulation is used, let's say, to extrapolate sea trial results because the ship is still under construction or is not complete. This can be seen as ‘performance indicators’, for example, to see 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.”
Continues Codda, “From my point of view, it is very important that we have the opportunity to validate our simulation and numerical models with experimental measurements and testing. This is still a vital step. In the marine industry, it is quite unusual that both the simulation and test experts work closely together in the same company. We have this luxury since we are the research center for Fincantieri. We have direct access to the ships, the test data and the validated simulations. This is not always the case throughout the marine industry.”
Codda concludes, “In the last decade, our role at CETENA has become ‘the selectors’ of the best technologies and mathematical models developed in the professional and academic community. We have to select and adapt available tools for the Fincantieri technical office. In some cases, we develop advanced design tools and models from existing software that the design office uses by themselves, such as the Simcenter Flomaster fire system model. In other cases, we develop more complex numerical procedures such, for example, the launching simulation. Simulation work like this is so complex and so computationally demanding that CETENA is still the best place to perform it.”