Goudsmit Magnetics becomes multiphysical

The Woolwich Ferry, near London, is crossing the Thames every six minutes and transfers more than two million passengers per year. Recently, the service had a major upgrade that made it unique in the world. The Intelligent Dock Locking system of Mampaey Offshore was installed, an automooring solution that replaces the regular method with ropes and bollards. Instead, the vessels are secured with huge magnets standing on the quay.

The magnetic system makes it possible to complete the mooring sequence in just ten seconds, even in the strongest river currents. The Intelligent Dock Locking system holds the vessel firmly in place, which enables the power to the ferry’s thrusters to be reduced to zero after docking, for the loading and unloading of passengers. This brings emissions down and saves costly fuel.

Key elements in the mooring system are the magnets, developed and engineered by Goudsmit Magnetics, from Waalre, the Netherlands. “For the two hydraulically controlled robot arms, we built a magnetic gripper, consisting of four magnetic plates of 70 by 70 centimeters each,” tells Cas van de Paal, product development engineer at Goudsmit. Every plate can withstand breakaway forces up to 80 kN. This is necessary to keep the vessel secured, regardless of the sway (about 320 kN) and surge (in practice 130 kN) caused by passing ships and the Thames’s current.

To achieve such a high gripping force, Goudsmit modeled the system extensively in the toolset from Comsol Multiphysics. “We took into account that there would be an air gap of 6 mm,” explains Van de Paal. “This is caused by the saltwater-resistant coatings, the friction pads and the unevenness in the docking plates. By applying an FMEA approach early in the process, we could minimize the design risks. FEM calculations with Comsol gave us additional insights into how to realize the system.”

Next to modeling the magnetic system, Goudsmit was asked to make mechanical calculations as well. Van de Paal: “Combining two physical properties in one calculation was almost impossible a decade ago. But Comsol set the trend by bringing all physics together in one tool, allowing truly multiphysical calculations.”

Milk

The mooring application it developed for Mampaey is a good example of how the magnetic solutions from Goudsmit tend to get multiphysical. It’s a trend the company saw coming several years ago. “In 2016, we started using Comsol for 3D FEM tooling, to model, simulate and optimize our products”, explains Martijn Leskens, product development engineer and team lead at Goudsmit. “The tool we used before for magnetic calculations lacked the possibility to extend our scope outside of the magnetic world.”

As another example of why Goudsmit switched to Comsol, Leskens tells about the separation applications his company develops. “Producers in the food or pharmaceutical industry, for instance, are very keen to prevent metal particles from getting in their end products. We develop magnetic filters that are used in the production of milk, amongst other things. The magnets are placed in the flow to capture the metal particles that pass by.”

To calculate the separation performance you need in that filter, it’s not enough to look solely at the magnetic aspects. “Flow is just as important,” states Leskens. “We didn’t have the capability of combining magnetic field and flow calculations. This changed with the switch to Comsol. And we can even predict how the particles behave within the flow, which is also crucial when you want to check the efficiency of your filter. For every filter configuration, we can forecast the percentage of particles it will catch. Of course, it’s still an estimation, as it’s only a model, but we can compare different setups and choose the best one.”

Pioneering Spirit

Comsol Multiphysics offers modules for magnetic, mechanical and flow calculations, covered in the two examples above. Goudsmit also uses the Comsol module for temperature analysis. This comes in handy when the company chooses an electromagnet, instead of a standard permanent magnet. “You can generate a magnetic field by applying a current to a coil,” explains Van de Paal. “Such an electromagnet has the benefit that you can switch the direction easily and determine the field steplessly. The downside is that you’re constantly using power, which often tips the balance to permanent magnets. Another disadvantage is that electromagnets will heat up due to the current. A higher current means a stronger field, but it also means more heat. And when a magnet gets hot, the field will diminish. We simulate this process in Comsol.”

To make it more concrete, Van de Paal tells about a project Goudsmit has been involved in: the Pioneering Spirit. Owned by Swiss-Dutch offshore contractor Allseas, it’s the largest construction vessel in the world. Its job is to install and remove lathe offshore platforms and lay the largest and heaviest subsea pipelines on the seabed. For pipelay, an onboard factory welds pipe sections together, which are lowered under tension onto the sea floor.

“As with every metal, these pipes can hold some residual magnetism,” elaborates Van de Paal. “This remanence might be limited, but it can seriously hamper the welding process. The electric arc contains electrons that are deflected by only the smallest magnetic field, causing a bad weld that won’t pass the strong quality checks.”

Goudsmit developed a demagnetization system to remove all residual magnetism from the pipes. “To calculate the necessary magnetic field, many factors play a role,” says Van de Paal. “The thickness of the pipes determines how strong the field needs to be. Demagnetization is done with an alternating field. The lower the frequency, the deeper it will penetrate. But a lower frequency also means a lower throughput. And since we’re working with a changing magnetic field, temperature is an issue. To get to the optimal result, we’ve modeled, simulated and calculated everything in Comsol, again by combining more fields of physics into one.”

This article was written in close collaboration with Comsol.