|Suandar Baso||Naval Architecture Department, Faculty of Engineering, Hasanuddin University, Jl. Perintis Kemerdekaan Km.10, 90245, Makassar, Indonesia|
|Hidemi Mutsuda||Division of Energy and Environmental Engineering, Faculty of Engineering, Hiroshima University, 1-4-1 Kagamiyama, Higashi-Hiroshima, 739-827, Hiroshima, Japan|
|Yasuaki Doi||Division of Energy and Environmental Engineering, Faculty of Engineering, Hiroshima University, 1-4-1 Kagamiyama, Higashi-Hiroshima, 739-827, Hiroshima, Japan|
Improving a ship’s stern part could help to reduce greenhouse gases and costs. However, a ship sailing in actual conditions experiences disturbances that can affect its performance. Ship performance is an important aspect of the design process that guarantees ship safety. The heave and pitch motions of an improved fishing boat were predicted numerically by using a hybrid scheme of Eulerian grid-Lagrangian particle, hereinafter improving its stern part and attaching an additional part. The stern part improvement and additional structure attachment affected an increase on the heave amplitude from the ship’s basic form by 5% to 10%. Moreover, the improvement of the stern part in the bottom area contributed to a better heave amplitude than that of the side area. Finally, the pitch amplitude for all forms was relatively small and affected an increase of 5% to 9%, dependent on the form. The improvement had a greater effect on heave motion than pitch.
Additional structure attachment; Heave motion; Hybrid particle-grid scheme; Pitch motion; Stern part improvement
Energy efficiency has drawn global attention to the decarbonizing of economies, the securing of energy supplies, and the increasing of productivity. This attention has involved the marine engineering field as well. To reduce ships’ greenhouse gas emissions, the International Maritime Organization (IMO) has urged the Marine Environment Protection Committee (MEPC) to identify and develop mechanisms to achieve such a reduction (IMO, 2010). To this end, the MEPC has introduced regulations focused on the limitation of CO2 production of newly built ships (MEPC, 2011). Optimization of the hull form and appendages are necessary to match these targets, which were both elaborated on by Legovic & Dejhalla (2016). This means that a ship’s geometry should be optimized appropriately due to its significant relation to ship performance and energy efficiency.
The resistance reduction improvements on the bow part of a fishing boat have been carried out by multiple researchers, such as Miyata et al. (1981), Miyata and Doi (1984), Suzuki et al. (1992), Kawashima et al. (2003) and Masuya (2007). However, few have been concerned with improvement on stern end bulb of Japanese fishing boats. Kim and Yang (2013), along with Gabor (2011), have recently conducted numerical works related to stern part improvement to reduce drag, and Supriadi et al. (2015) applied a replication of micro-riblets to a ship’s hull for drag reduction. That being said, the styles of fishing boats is known to vary as widely as fishing techniques.
Mutsuda et al. (2013) studied the numerical resistance reduction of fishing boats by improving the stern part. In this study, the improvement of the body line and the addition of a structure at the stern part was examined to reduce drag resistance. All of the cases proposed in this study could reduce water resistance with the maximum reduction rate of around 15 to 20% when compared with the ship’s basic form (original case). In addition, Suastika et al. (2017) studied the effects of a stern foil application on ship resistance by using a numerical method and comparing experimental results. Based on the results, applying a stern part foil to decrease ship resistance obtained an effect at high speed (Fr ? 0.5), decreasing ship resistance up to 10.0%. By contrast, properly designed bulbous bows have been proven to reduce resistance by 15% to 40%, depending on the steaming speed, overall hull proportions, etc. (Friis et al., 2010, 2017).
Shenglong et al. (2018) optimized the hull form of a ship in waves, based on a CFD technique, but, the motions of pitch and heave were not computed and only the ship motion was facilitated by the CFD technique. Kim et al. (2010) also optimized a hull form for reduced resistance and improved seakeeping via practical design-oriented CFD tools. In this paper, resistance reduction is clearly explained and obtained. However, the evaluation of seakeeping using the Bales’ Ranking method could only quantify one wave condition (Kim et al., 2010). The improvement of ship form, such as that of fishing boats, must also contribute to good performance in a seaway, forcing designers to improve ship performance, such as reducing ship response or motion. Therefore, we continue the study (Mutsuda et al., 2013) by focusing on the motions of fishing boats as result of stern part improvement using a hybrid scheme or hybrid Eulerian grid with Lagrangian particle scheme. The improvement of the stern part in the bottom area enhances the heave amplitude while the pitch amplitude for all forms is relatively small and increases by 5% to 9%, depending on the form. Some snapshots caused by nonlinear interactions between ship-wave could be captured clearly.
In this study, the heave and pitch motions of a ship were predicted using a hybrid Eulerian grid with Lagrangian particle scheme. The stern part improvements and the additional structure attachments affected an increase on the heave amplitude from the ship’s basic form of 5% to 10%, but the heave amplitude was insignificant if the form differed slightly. Moreover, the improvement of the stern part in the bottom area contributed to a better heave amplitude than the side area improvement. The pitch amplitude for all forms was relatively small and was increased by 5% to 9%, depending on the form. The improvement showed a greater effect on the heave motion than on the pitch motion, but all forms were acceptable based on motion amplitude. The stern part improvement influenced slight motion response in contrast with resistance reduction. The developed numerical method (Baso et al., 2011; Mutsuda et al., 2013) of a hybrid Eulerian grid with Lagrangian particle could be used practically in the preliminary ship design stage.
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