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Trawl-door Performance Analysis and Design Optimization with CFD
Eirikur Jonsson, Leifur Leifsson and Slawomir Koziel
Engineering Optimization & Modeling Center, School of Science and Engineering, Reykjavik University, Reykjavik, Iceland
Keywords:
Trawl-doors, CFD, Design Optimization, Space Mapping, Surrogate-based Optimization, Variable-resolution
Modeling, Simulation-driven Design.
Abstract:
Rising fuel prices and inefficient fishing gear are hampering the fishing industry. In this paper, we present a
computational fluid dynamic (CFD) model to analyse the hydrodynamic performance of trawl-doors, which
are a major contributor to the high fuel consumption of fishing vessels. Furthermore, we couple the CFD
model with an efficient design optimization technique and demonstrate how to redesign the trawl-door shapes
for minimum drag at a given lift. The optimization techinique is surrogate-based and employs a coarse discriti-
zation CFD model with relaxed convergence criteria. The surrogate model is constructed using the physics-
based low-fidelity model and space mapping. The CFD model is applied to the analysis of current trawl-door
shapes and reveals that they are operated at low efficiency (with lift-to-drag ratios lower than 1), mainly due to
massively separated flow. An example design optimization case study reveals that the angle of attack can be
reduced significantly by re-positioning and tilting the leading-edge slats. The performance can be improved
by as much as 24 times (attaining lift-ro-drag ratios around 24).
1 INTRODUCTION
Efficient trawler ships are vital for the fishing indus-
try. Rising fuel prices have an enormous impact on
the fishing industry as a whole as the cost of fuel is a
major part of the operation cost. Most of the fuel (of-
ten over 80%) is spent during the trawling operation,
which can take days at a time, although the trawling is
normally performed at low speeds (less than 3 knots).
The reason is the high drag of the fishing gear assem-
bly. Therefore, a careful study and redesign of the
assembly is necessary in order to reduce the fuel con-
sumption and improve the efficiency.
A typical fishing gear assembly, shown in Fig. 1,
consists of a large net, a pair of trawl-doors to keep
the net open, and a cable assembly extending from
the trawl-doors to the boat and the net. Although
the trawl-doors are a small part of the fishing gear,
they are responsible for roughly 30% of the total drag
(Garner, 1967). A typical trawl-door is shown in Fig.
2.
Almost all the trawl-doors that have been de-
veloped over the years are fundamentally the same.
Trawl-door designs are essentially steel plates, cut
down, bent with a certain radius and welded together.
These designs have two key elements, namely, the
main element (ME), which is the largest part, and one
or more slats or slots, located at the leading edge. Mi-
nor design changes have been made to trawl-doors
over the years, mainly because their designs are solely
based on time consuming and expensive physical ex-
periments.
Although, computational fluid dynamics (CFD) is
widely used in design of a variety of engineering de-
vices, such as aircraft, ships, and cars, very few ap-
plications are reported for trawl-doors in the litera-
ture (Haraldsson et al., 1996). Therefore, there is
an opportunity to apply state-of-the-art CFD methods
and optimizatin techniques to analyse and redesign
the trawl-doors, before using physical experiments for
verification purposes only. The trawl-doors have a
low aspect ratio and are operated at high angles of
attack (up to 50 degrees). As a result, the flow is
highly three-dimensional and transient. A full three-
dimensional simulation is required to capture the flow
physics accurately. However, such simulation can be
time consuming, and if used directly within the op-
timization loop (requiring a large number of simula-
tions), the overall time of the design process becomes
prohibitive. An efficient design methodology is there-
fore essential for such design applications.
In this paper, we develop a robust high-fidelity
CFD method for the performance analysis of trawl-
doors. As a first step in this development, we use
479
Jonsson E., Leifsson L. and Koziel S..
Trawl-door Performance Analysis and Design Optimization with CFD.
DOI: 10.5220/0004163904790488
In Proceedings of the 2nd International Conference on Simulation and Modeling Methodologies, Technologies and Applications (SDDOM-2012), pages
479-488
ISBN: 978-989-8565-20-4
Copyright
c
2012 SCITEPRESS (Science and Technology Publications, Lda.)