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Exploring the effects of speed and scale on a ship’s form factor using CFD
Terziev Momchil,Tezdogan Tahsin,Demirel Yigit Kemal,Villa Diego,Mizzi Simon,Incecik Atilla 대한조선학회 2021 International Journal of Naval Architecture and Oc Vol.13 No.1
The problem of predicting a ship’s form factor and associated scale effects has been subject to many investigations in recent years. In this study, an attempt is made to investigate whether the form factor is influenced by a change in the ship’s speed by numerically modelling a geosim series of the KCS hull form by means of a RANS solver. The turbulence dependence of the problem is also studied by altering the closure model among three widely used approaches (the k-ω, k-ω SST, and k-ε models). The results show that at very low speeds (Froude numbers in the range of 0.02–0.06) the numerical model predicts changes in the form factor of a ship between 10% and 20%, depending on the turbulence model and scale factor choices. As the speed is increased further, the form factor exhibits little change, usually in the range of 1% or less. Simulations where the Reynolds number is changed by approximately two orders of magnitude, achieved by altering the value of viscosity, confirmed that the form factor can be considered Froude-dependent only for low speeds, predicting essentially identical values when high speed cases are considered.
Numerical investigation of depth-varying currents on ship hydrodynamics in confined water
Terziev Momchil,Tezdogan Tahsin,Demirel Yigit Kemal,De Marco Muscat-Fenech Claire,Incecik Atilla 대한조선학회 2022 International Journal of Naval Architecture and Oc Vol.14 No.1
Vessels can operate in unpredictable environments depending on the geographical area and weather conditions. One example of conditions a vessel might not be assessed against is the presence of depthvarying currents, which are particularly relevant in confined waters where currents can be created due to tidal influences, or short fetches in inland waterways. The possible presence of depth-varying currents motivates a numerical assessment of the effects of sheared currents on the hydrodynamic performance of the KRISO Container Ship (KCS) in confined waters. The results highlight that exploiting currents, such as those generated by tides could be used to improve the energy efficiency of vessels considerably. These currents present significant possibilities for voyage optimisation based on geographical and meteorological conditions. The results specific for the KRISO container ship point to resistance reductions when the current assists ship motions, accompanied by considerable decreases in sinkage and trim. Conversely, when currents oppose ship motion, resistance, sinkage and trim can increase by a factor of 3 depending on the strength and shape of the depth-varying current. The results also show that a current with constant vorticity, a case frequently used in the literature to investigate the impact of sheared currents, creates the biggest increase and decrease for inhibiting and assisting currents, respectively.
Bilge keel design for the traditional fishing boats of Indonesia's East Java
Liu, Wendi,Demirel, Yigit Kemal,Djatmiko, Eko Budi,Nugroho, Setyo,Tezdogan, Tahsin,Kurt, Rafet Emek,Supomo, Heri,Baihaqi, Imam,Yuan, Zhiming,Incecik, Atilla The Society of Naval Architects of Korea 2019 International Journal of Naval Architecture and Oc Vol.11 No.1
Seakeeping, especially for the roll motions, is of critical importance to the safe operation of fishing boats in Indonesia. In this study, a traditional East Java Fishing Boat (EJFB) has been analysed in terms of its seakeeping performance. Furthermore, a bilge keel was designed to reduce the roll motions of the EJFB using multiple stages approach. After installing the designed bilge keels, it was shown that up to 11.78% and 4.87% reduction in the roll response of irregular seaways and the total resistance under the design speed, respectively. It was concluded that the roll-stabilized-EJFB will enhance the well-being of the fisherman and contribute to the boats' safe operation, especially in extreme weather conditions. Moreover, the total resistance reduction of the EJFB due to the installation of the designed bilge keels also resulted in increased operational efficiency and reduced fuel costs and fuel emissions for local stakeholders.
Bilge keel design for the traditional fishing boats of Indonesia's East Java
Wendi Liu,Yigit Kemal Demirel,Eko Budi Djatmiko,Setyo Nugroho,Tahsin Tezdogan,Rafet Emek Kurt,Heri Supomo,Imam Baihaqi,Zhiming Yuan,Atilla Incecik 대한조선학회 2019 International Journal of Naval Architecture and Oc Vol.11 No.1
Seakeeping, especially for the roll motions, is of critical importance to the safe operation of fishing boats in Indonesia. In this study, a traditional East Java Fishing Boat (EJFB) has been analysed in terms of its seakeeping performance. Furthermore, a bilge keel was designed to reduce the roll motions of the EJFB using multiple stages approach. After installing the designed bilge keels, it was shown that up to 11.78% and 4.87% reduction in the roll response of irregular seaways and the total resistance under the design speed, respectively. It was concluded that the roll-stabilized-EJFB will enhance the well-being of the fisherman and contribute to the boats' safe operation, especially in extreme weather conditions. Moreover, the total resistance reduction of the EJFB due to the installation of the designed bilge keels also resulted in increased operational efficiency and reduced fuel costs and fuel emissions for local stakeholders.
김대정,Song Soonseok,Sant Tonio,Demirel Yigit Kemal,Tezdogan Tahsin 대한조선학회 2022 International Journal of Naval Architecture and Oc Vol.14 No.1
The loss of ship propulsion has been reported to be the most frequent cause of accidents at sea over the last few years. The loss of propulsive power has a notable effect on the behaviour of a ship during ship manoeuvring, and hence the manoeuvrability of ships suffering from propulsion loss should be accurately estimated for navigation safety. The aim of this study is to evaluate the effects of a propulsion failure on the manoeuvrability of the KRISO Container Ship (KCS) using a fully nonlinear URANS model, which is capable of resolving complex fluid-structure interactions with high accuracy. A series of case studies were carried out to compare the ship performances of both the normal and propulsion loss condition, especially for the course keeping and turning circle manoeuvres. The results explicitly revealed that the propulsion failure has a strong influence on the ship manoeuvrability, implying the importance of sufficient propulsion power when vessels are underway. The key findings obtained from this study are believed to provide navigators with a practical insight into ship manoeuvrability under the propulsion failure condition as well as contribute to developing standards for navigational safety in waves.