Significance of seabed interaction on fatigue assessment of steel catenary risers in the touchdown zone

Hany Elosta,Shan Huang,Atilla Incecik 국제구조공학회 2016 Structural Engineering and Mechanics, An Int'l Jou Vol.57 No.3

The challenges involved with fatigue damage assessment of steel catenary riser (SCR) in the touchdown zone (TDZ) are primarily due to the non-linear behaviour of the SCR-seabed interaction, considerable uncertainty in SCR-seabed interaction modelling and geotechnical parameters. The issue of fatigue damage induced by the cyclic movements of the SCR with the seabed has acquired prominence with the touch down point (TDP) interaction in the TDZ. Therefore, the SCR-seabed response is critical for reliable estimation of fatigue life in the TDZ. Various design approaches pertaining to the lateral pipe-soil resistance model are discussed. These techniques have been applied in the finite element model that can be used to analyse the lateral SCR-seabed interaction under hydrodynamic loading. This study investigates the sensitivity of fatigue performance to geotechnical parameters through a parametric study. In this study, global analyses are performed to assess the influence of vertical linear seabed springs, the lateral seabed model and the non-linear seabed model, including trench evolution into seabed, seabed normalised stiffness, re-penetration offset parameter and soil suction resistance ratio, on the fatigue life of SCRs in the TDZ.

Numerical studies on non-linearity of added resistance and ship motions of KVLCC2 in short and long waves

Olgun Hizir,Mingyu Kim,Osman Turan,Alexander Day,Atilla Incecik,Yongwon Lee 대한조선학회 2019 International Journal of Naval Architecture and Oc Vol.11 No.1

In this study, numerical simulations for the prediction of added resistance for KVLCC2 with varying wave steepness are performed using a Computational Fluid Dynamics (CFD) method and a 3-D linear potential method, and then the non-linearities of added resistance and ship motions are investigated in regular short and long waves. Firstly, grid convergence tests in short and long waves are carried out to establish an optimal mesh system for CFD simulations. Secondly, numerical simulations are performed to predict ship added resistance and vertical motion responses in short and long waves and the results are verified using the available experimental data. Finally, the non-linearities of added resistance and ship motions with unsteady wave patterns in the time domain are investigated with the increase in wave steepness in both short and long waves. The present systematic study demonstrates that the numerical results have a reasonable agreement with the experimental data and emphasizes the non-linearity in the prediction of the added resistance and the ship motions with the increasing wave steepness in short and long waves.

Numerical studies on non-linearity of added resistance and ship motions of KVLCC2 in short and long waves

Hizir, Olgun,Kim, Mingyu,Turan, Osman,Day, Alexander,Incecik, Atilla,Lee, Yongwon The Society of Naval Architects of Korea 2019 International Journal of Naval Architecture and Oc Vol.11 No.1

In this study, numerical simulations for the prediction of added resistance for KVLCC2 with varying wave steepness are performed using a Computational Fluid Dynamics (CFD) method and a 3-D linear potential method, and then the non-linearities of added resistance and ship motions are investigated in regular short and long waves. Firstly, grid convergence tests in short and long waves are carried out to establish an optimal mesh system for CFD simulations. Secondly, numerical simulations are performed to predict ship added resistance and vertical motion responses in short and long waves and the results are verified using the available experimental data. Finally, the non-linearities of added resistance and ship motions with unsteady wave patterns in the time domain are investigated with the increase in wave steepness in both short and long waves. The present systematic study demonstrates that the numerical results have a reasonable agreement with the experimental data and emphasizes the non-linearity in the prediction of the added resistance and the ship motions with the increasing wave steepness in short and long waves.

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.