Photo: Joachim Rode

Knowledge of wave energy can result in more eco-friendly shipping

Friday 01 Mar 19
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Ulrik Dam Nielsen
Associate Professor, Dr.techn.
DTU Mechanical Engineering
+45 45 25 19 70
Doctoral Dissertation: Ulrik Dam Nielsen sheds new light on the measurement of wave energy and the impact ships are exposed to during voyages at sea.

Anyone who has ever swum in the North Sea can attest to the immense power of the waves. Wave energy is often even greater at sea—a fact that has major implications for all types of shipping.

As a researcher at DTU Mechanical Engineering, Ulrik Dam Nielsen has for many years worked on methods to calculate and predict how ocean waves affect shipping and other floating structures at sea. This research has now formed the basis for a doctoral dissertation which he presented on 7 February.

Knowledge of the size and extent of the waves—i.e. the wave energy in the form of wave spectra—is essential in connection with calculations of ship safety and fuel consumption. The dissertation is therefore a significant step forward in the efforts to optimize fuel consumption and improve safety on today’s manned vessels and autonomous ships of the future.

“Armed with precise information about wave energy in the areas where their ships are sailing, shipping companies will have a more precise analysis of their ships’ fuel consumption. Typically, shipping companies order an estimate of the weather conditions in a wide area around their ships from a meteorological institute. Such estimates, however, may be quite inaccurate, as the individual ship’s position rarely matches exactly with the estimate site,” says the new Dr.Techn.

“In addition, the estimate doesn’t arrive until several days later. The objective of my research, therefore, is to establish methods that improve wave energy estimation using measurable ship movements based on the ship’s exact position and moment in time.”

"Generally, there is more focus on monitoring the individual ships’ performance in order to optimize efficiency. "
Ulrik Dam Nielsen, DTU Mechanical Engineering

A container ship at sea encounters resistance from still water and from the waves. Over the past 10 to 15 years, shipping companies have focused increasingly on the environment and fuel economy. Among other things, this has resulted in container vessels in particular sailing significantly slower than previously. While this has considerably reduced still-water resistance, the resistance caused by the movement of the ships through the waves has proportionally increased. It is therefore important to have detailed knowledge about the size and extent of the waves.

“Generally, there is more focus on monitoring the individual ships’ performance in order to optimize efficiency. For example, the propeller and hull are exposed to wear and tear and various biological microorganisms, which increases resistance. If we know exactly what kind of waves the ship is exposed to in different stretches of ocean, shipping companies can more accurately calculate whether poor performance is due to weather conditions—or whether the hull needs to be cleaned,” explains Ulrik

Wave estimation increases safety
The scientific estimation of wave energy has the potential to do more than optimize fuel consumption—it can also improve safety conditions on ships and in connection with the construction and maintenance of various offshore constructions. With accurate wave energy data, so-called operations windows can be established, indicating, for example, whether it is safe to carry out a lifting operation from a crane vessel.

“A captain or an autonomous ship can navigate through a rough sea with greater certainty if there are reliable wave data available during the voyage,” says Ulrik Dam Nielsen, and continues:

“You have similar problems within the offshore industry where you are installing and maintaining wind turbines and marine fishery installations. The crews work with operations windows and want to know whether they can safely carry out an operation in the next 30-60 minutes. And the only way of knowing this is to have reliable wave data.”

Photo: Joachim Rode

Future perspectives
Since completing his PhD in 2002-2005, Ulrik has worked as a researcher and associate professor at DTU Mechanical Engineering. Here, he has regularly collected data and findings from his wave estimation research which he has used in his dissertation.

“I think it’s interesting to work with issues relating to ships and ship operation at sea, and the interrelationship between ship and waves is key when using a ship as a floating wave buoy—i.e. for wave estimation.

Another element is that this knowledge still hasn’t been implemented on a commercial scale. I therefore hope that my doctoral dissertation is a step towards making ships of the future and their operations safer and more eco-friendly.”