Determining and predicting the seakeeping performance of ships based on jerk in the ship motions

Determining and predicting the seakeeping performance of ships based on jerk in the ship motions

Werkman, Joren (TU Delft Mechanical, Maritime and Materials Engineering; TU Delft Ship Hydromechanics and Structures)

Westerweel, Jerry (mentor)
Schreier, Sebastian (mentor)
Visser, Klaas (graduation committee)
Bottger, Amarante (graduation committee)
Sigmund, Sebastian (mentor)

Delft University of Technology

Marine Technology | Hydromechanics

2019-07-31

The comfort assessment of ships is based on several criteria. There are for example criteria for motions, noise and vibrations. The criteria for motions are nowadays often defined as comfort limits on the accelerations in the ship motions. However, from other industries it followed that the rate of change of the accelerations, the jerk, can also have an influence on the sense of comfort of passengers and crew. The goal of this thesis is to investigate whether it would be useful to add jerk criteria to the comfort assessment of ships. Jerk cannot be measured directly (yet), so it has to be obtained from acceleration measurements or calculations. For this goal filter and processing procedures are defined. To be able to make comparisons different ways of quantifying the jerk are established. One is aimed at peak values, since these are often determining the limit for comfort and operability. The other is focused on quantifying the non-linearity of the response. Research is performed on what the physics behind jerk are, and what phenomena are likely to cause large jerk values. The prime cause is found in slamming. The jerk following from slamming is influenced mostly by the shape of the bow and the speed of immersion in the water. Using the measurement data of two different hulls from other research the effect of varying conditions on the jerk is investigated. From this research it follows that there can be a difference in seakeeping behaviour when looking at jerk instead of accelerations. Since jerk is the third derivative of displacement to time, the non-linearity in this response is relatively high. Therefore non-linear codes are required to calculate the jerk response correctly. The use of a Reynolds Averaged Navier Stokes (RANS) code proves to be able to predict the jerk behaviour correctly. In this thesis only model test measurements and calculations are used. The scaling of jerk to full scale, and difficulties that it might impose, are only discussed theoretically. The general conclusion is that jerk is worth investigating to compare the seakeeping behaviour of ships. Until quantitative limits are available only qualitative comparisons are possible, but these can already give additional insight.

Ship motion
Jerk
Seakeeping
Ship comfort
Ship response
Non-linearity
Hydromechanics
Slamming

http://resolver.tudelft.nl/uuid:fff9699e-1c41-41d1-bc9a-1f2ff347a0a1

Student theses

master thesis

© 2019 Joren Werkman