Published at : 19 Jul 2021
Volume : IJtech
Vol 12, No 3 (2021)
DOI : https://doi.org/10.14716/ijtech.v12i3.4659
I Ketut Aria Pria Utama | Department of Naval Architecture, Faculty of Marine Technology, Institut Teknologi Sepuluh Nopember, Kampus ITS Sukolilo, Surabaya 60111, Indonesia |
Sutiyo | Department of Naval Architecture, Faculty of Engineering and Marine Science, University of Hang Tuah, Jalan Arief Rahman Hakim 150, Surabaya 60111, Indonesia |
Ketut Suastika | Department of Naval Architecture, Faculty of Marine Technology, Institut Teknologi Sepuluh Nopember, Kampus ITS Sukolilo, Surabaya 60111, Indonesia |
Using the axe-bow to
reduce total ship resistance on monohull ships has been well-known. This
advantage has been further applied to a trimaran configuration together with
its space-to-length (S/L) ratio differences. The investigation was carried out
experimentally using an ITTC standard towing tank and numerically using
computational fluid dynamics (CFD) analysis. The base model for the study uses
an NPL 4a both for the mainhull and sidehulls of the trimaran, and later the
mainhull is modified by attaching a front bulb known as an axe-bow. The
resistance analysis of the trimaran was conducted with and without an axe-bow
on the mainhull together with S/L ratios of S/L = 0.3 and S/L = 0.4 and at
various Froude (Fr) numbers: 0.15, 0.2, 0.25, 0.3, 0.4, and 0.5. The results
showed that the monohull with an axe-bow had a smaller drag than that without
an axe-bow of an order up to 11.5%, whereas in the trimaran form, the reduction
of drag was up to 8.4%. This indicates a positive influence of using the
axe-bow on the total resistance of the trimaran configuration. Both
experimental and CFD methods showed positive agreement of the order 2.7%
discrepancy for the monohull form and a 3.4% discrepancy for the trimaran
configuration.
Axe-Bow; CFD; Experiment; NPL; Resistance; Trimaran
There is increased interest in
trimaran vessels due to their advantages and applications (Elcin, 2003). The trimaran
has sidehulls for gaining ship stability. Three hulls make the trimaran
completely unsinkable. Even in the roughest weather, the ultimate hazard of
capsizing is minimized. Mainhulls and sidehulls can be modified flexibly to
reduce resistance (Sulistyawati and Suranto, 2020). Therefore,
the decrease in trimaran resistance results in reducing fuel consumption
compared to an equivalent monohull.
In
recent decades, much research has considered the advantages of the trimaran
concept. When the literature on trimarans is examined in general, it is clear
that the most important parameter in resistance optimization is configuring the
outriggers because of the flow-interference effect between the center-hull and
outriggers (Yildiz et al., 2020). Optimum placement of these will result in an interaction
between the wave train produced by the center-hull and the wave trains produced
by the outriggers that ideally counteract each other at primary speed(s) of
interest (Chen et al., 2016).
Preliminary
research on trimarans was carried out by Gray (2003). In this
study, resistance characteristics of a trimaran hull form with different
arrangements were investigated to verify the theoretical prediction by
comparing towing test results. The CFD method was
utilized by Javanmardi et al. (2008)
to analyze the hydrodynamic performance of the trimaran hull form with
small-sized outriggers to determine optimum outrigger positions
for minimum wave resistance performance. They also
considered the wave interactions between the center-hull and outriggers to predict
total wave-making resistance.
Shahid and Huang (2011)
investigated the prediction of wave resistance on trimaran hull forms using CFD
software. Three different mesh sizes and two different turbulence models were
used to investigate the effect of mesh structure and turbulence models on the
prediction of the resistance. CFD analyses were realized corresponding to
Froude number ranges from 0.14 to 0.75, and the results were compared with the
experimental data. Son (2015) performed
CFD computations of a systematic series of trimaran hull forms. The center-hull
form of the trimaran was developed based on the National Physical Laboratory (NPL)
systematic series of round bilge hulls, and the sidehulls were created by
scaling the center-hull to one-third size. Poundra et al. (2017) explained
that the placement of the sidehull greatly affects ship resistance, both
longitudinally and transversely. Catamaran hull interference can reduce
resistance, as discussed by Iqbal and Samuel (2017) and Utama et al. (2021). This
interference phenomenon also occurs in a more complex form on trimaran ships.
The interaction between the hulls on a trimaran ship is examined by Sun et al. (2020), who prove
that the ?ow ?eld between the mainhull and sidehull of the trimaran can be
captured by numerical calculations and PIV tests of the microscopic and
macroscopic structures of the ?ow ?eld. Trimaran configurations with proper
positions can reduce residual resistance values (Heidari et al., 2019, Yanuar et al., 2020; Yildiz et al., 2020).
Further, the development of hull
optimalization was carried out using the axe-bow. It uses straight vertical
sides to dampen waves from the bow, which can result in a smooth pitching
motion. Basically, the axe-bow in the extended section is empty space. The
study of the axe-bow shows an increase in efficiency and a reduction in pitch
acceleration because ships with axe-bows have less resistance in conventional
models and reduce fuel use (Gelling, 2006).
The axe-bow developed by Damen Shipyard
has better efficiency as well as better head-sea performance, with less
slamming and higher speeds (Buckley, 2010). Damen Shipyard (2012) made a
delivery of the first ship with an axe-bow, the Patrol Boat. The ship exhibits
effective movement behavior and significantly lower drag while sailing. This provides
a 20% reduction in fuel use and, consequently, fewer emissions. Through the CFD
analysis of the optimum hull, it was possible to con?rm the reduction of added
resistance by the re?ected wave around the bow smoothly spread to the side (Seok et al., 2019).
Two advantages to reducing ship
resistance using the trimaran hull and the axe-bow have been mentioned in the
previous literature. This paper discusses a combination of the two to obtain a
better resistance reduction.
An investigation into
the effect of using the axe-bow on the resistance reduction of the trimaran
configuration has been carried out numerically using the CFD approach and
experimentally using an ITTC standard towing tank. The study was conducted
using an NPL 4a model with and without the axe-bow on both the monohull and
trimaran models with variations of S/L = 0.3 and 0.4. The use of CFD makes a
very good contribution in relation to the calculation of resistance on monohull
and trimaran vessels, both for NPL 4a and NPL 4a with the axe-bow. These
results have been verified using experimental data with a discrepancy
of about 2.7% on the monohull to 3.4% on the trimaran mode. Using the axe-bow gave a positive contribution, a
reduction of up to 11.5% when compared to conventional hulls. Drag reduction of
the ship is the ability of the axe-bow to reduce wave-making due to the
interaction of the bow and water. In the trimaran mode with variations of S/L =
0.3 and 0.4, the mainhull with the axe-bow was able to contribute to the
reduction of resistance of up to 8.4%. This reduction in resistance occurs due
to the contribution of the axe-bow, which can reduce wave-making in the bow,
which further reduces the hull interaction.
The authors wish to thank the Directorate of
Research and Community Services (DRPM) ITS for financing the research under a
research scheme called “Postgraduate Research Grant” with contract number
920/PKS/ITS/2020. The authors also thank Mr. Langgeng Condro and Mr. Rudie
Aminudin from the ITS Laboratory of Hydrodynamics for their help in the
experimental test of the trimaran resistance.
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