Investigating the Feasibility of Electromechanical Actuation in a Submarine

Abstract

Traditionally hydraulic actuators has been the primary choice in modern submarines due to their strength and reliability. In recent years many commercial and military vehicles have switched to electromechanical alternatives, as they are generally more energy efficient and have superior controllability. These are two attributes valued in a submarine, hence an investigation was carried out to assess the possibility of making a switch to electromechanical actuators in submarine.

The actuators, cylinders and rotary valve actuators, investigated were chosen as they are prevalent in a submarine and a substitution would hence make a significant difference in energy consumption. Apart from energy consumption the actuators were also evaluated in terms of acoustics, which includes sound and vibrations, as well as electromagnetic compatibility (EMC). These parameters
are important to not emit signals that can reveal the position of the submarine.

A theoretical analysis was performed using component data sheets, to see whether electrical actuators would be more energy efficient than their hydraulic counterparts. The analysis showed that rotary valve actuators were more energy efficient. A switch to electric cylinders only become energy efficient if enough of them are replaced to warrant a reduction in hydraulic pump size. Additionally
it was found to be more advantageous to replace smaller hydraulic actuators with electrical. As the force and torque requirements increase the size and operating time of the electrical actuators increase more than the hydraulic counterparts. Furthermore: compartments with a low change of being submerged in water and lower demands of redundancy are deemed to be optimal for a substitution to electrical actuators.

As mentioned energy efficiency is not the only aspect to consider for a switch to electrical actuators. To evaluate EMC and acoustics practical tests were conducted, the former only on the electrical components. None of the electrical actuators passed all of the EMC requirements. The components exceeded the requirements at low frequencies which are hard to attenuate with just
filters and shielding. In the sound test only small differences between the hydraulic and electric actuators were seen. However, in the vibration tests which is of higher importance as vibrations easily propagate through the structure, the hydraulic components performed better.

The recommendation, based on the results of this project, is to look into electrical rotary valve actuators which are approved for military use and replace as many as possible. However, caution has to be taken when replacing safety critical functions since, the fail-safe capabilities of a hydraulic system is more robust than for the individual electrical actuators.

Popular Abstract

With the Baltic sea becoming a region with contested borders, submarines that can undertake long missions to patrol the seas and deter altercations are crucial. The hydraulic system currently used in modern day submarines, while reliable, is a potential fire hazard and not necessarily the most energy efficient
solution. Recent developments have made electromechanical actuators
more energy efficient than their hydraulic counterparts, enabling longer missions. It is therefore of great interest for Swedish submarine giant, Saab Kockums, to investigate the possibility of replacing or scaling down the hydraulic system.

Due to the high power density and small size of the hydraulic components, they have been the premier choice for actuation in submarines. The goal of the project was to see whether hydraulic components could be replaced by electromechanical counterparts.

Two types of actuators were decided to be investigated: cylinders and rotary valve actuators.

One of the big advantages of electromechanical actuators is their high efficiency due to fewer steps of energy conversion. A drawback to the hydraulic system is that the main pump is always active. This due to the risk of the loud sounds associated with turning off and on the pump spreading out into the water, thus revealing the submarine's position. Therefore, the hydraulic system will
continuously draw power even when no control action is needed.

Calculations show that hydraulic cylinders that rarely run are most suitable for
replacement by electric counterparts while rotary valve actuators are even more
efficient and would improve the energy efficiency of the submarine wherever
implemented. The often running rotary valve actuators would be especially
beneficial to implement because the hydraulic pump is always active. By replacing hydraulic valve actuators, the pump can be downsized to draw less power in its idle state.

The tests carried out: Electromagnetic compatibility (EMC), sound and vibrations, highlight some of the inherent problems with electromechanical actuators. While all actuators tested passed the sound tests none passed the EMC and vibrations tests.

None of the components tested passed all the necessary requirements. However, the potential energy savings warrants further investigation into similar actuators. Finding these replacements could prove greatly beneficial in increasing the safety of the crew and opening up the possibility for longer missions, highlighting
the potential for a fleet of electric submarines safeguarding the Baltic Sea.

• author: Sundvall, Erik and Erliden, Carl
• supervisor: Ulf Jeppsson; Avo Reinap
• organization: Industrial Electrical Engineering and Automation
• alternative title: Undersöker möjligheten för användning av elektromekaniska ställdon i en ubåt
• course: EIEM01 20241
• year: 2024
• type: H3 - Professional qualifications (4 Years - )
• subject: Technology and Engineering
• publication/series: CODEN:LUTDEX/TEIE
• report number: 5509
• language: English
• id: 9166348
• date added to LUP: 2025-02-05 16:59:31
• date last changed: 2025-02-05 16:59:31