Artificial Neural Network Model for the Evaluation of Added Resistance of Container Ships in Head Waves

The decrease in ship added resistance in waves fits into both the technical and operational measures proposed by the IMO to reduce the emissions of harmful gases from ships. Namely, the added resistance in waves causes an increase in fuel consumption and the emission of harmful gases in order for the ship to maintain the design speed, especially in more severe sea states. For this reason, it is very important to estimate the added resistance in waves with sufficient accuracy in the preliminary design phase. In this paper, the possibility of applying an ANN to evaluate added resistance in waves at the different sea states that the ship will encounter during navigation is investigated. A numerical model, based on the results of hydrodynamic calculations in head waves, and ANN is developed. The model can estimate the added resistance of container ships with sufficient accuracy, based on the ship characteristics, sailing speed, and the sea state using two wave energy spectra.

Application of Energy Saving Bow Shape in Actual Seas to JBC

Energy Efficiency Design Index (EEDI) entered Phase 2 in 2020. In this situation, ship performance in actual seas is more important than ever. As an energy saving bow shape in actual seas, the authors are developing a bow shape named “COVE (Concave shape optimized in waves)”. The aim of COVE is to improve performance in waves without deteriorating performance in a calm sea by transformation above the static swell up at the target speed. Since the bow shape is concave above the static swell up, COVE reduces waves reflected forward because the most concave line has a fine triangular shape instead of the blunt shape of the original. In this paper, COVE is applied to a Capesize bulk carrier, the JBC (Japan Bulk Carrier). The parameters of COVE are examined and the shape is optimized for the JBC. The effect of COVE is validated by tank tests in terms of wave lengths, wave angles, wave heights and ship speeds. The results clarified the fact that COVE reduces added resistance in waves by approximately 30 % in head waves compared with the original shape. Validity was verified by the radiating wave shape and the side wall wave form recorded by a video camera in the tests.

Evaluation of the Effect of Container Ship Characteristics on Added Resistance in Waves

Added resistance in waves is one of the main causes of an increase in required power when a ship operates in actual service conditions. The assessment of added resistance in waves is important from both an economic and environmental point of view, owing to increasingly stringent rules set by the International Maritime Organization (IMO) with the aim to reduce CO2 emission by ships. For that reason, it is desirable to evaluate the added resistance in waves already in the preliminary ship design stage both in regular and irregular waves. Ships are traditionally designed and optimized with respect to calm water conditions. Within this research, the effect of prismatic coefficient, longitudinal position of the centre of buoyancy, trim, pitch radius of gyration, and ship speed on added resistance is investigated for the KCS (Kriso Container Ship) container ship in regular head waves and for different sea states. The calculations are performed using the 3D panel method based on Kelvin type Green function. The results for short waves are corrected to adequately take into account the diffraction component. The obtained results provide an insight into the effect of variation of ship characteristics on added resistance in waves.

Detailed Study on the Behavior of Ships in Very Short Waves

Considering the sea conditions in which a large ship encountered in operation, the ship’s behavior in very short waves is important. However, the evaluation of the ship performance in very short waves was not enough validated by tank tests. Because it is difficult to generate waves with enough accuracy due to the performance of the wave generator. In this paper, it is shown that tank tests of added resistance in the regular waves including the very short waves are conducted in the Actual Sea Model Basin at National Maritime Research Institute, MPAT for DTC container ship and accurate results are obtained. The test results are compared with the benchmarks published by SHOPERA (Energy Efficient Safe SHip OPERAtion). In addition, three curves of the added resistance in the regular waves based on the results of the tank test are compared and the sensitivity analysis of energy efficiency is discussed. In the sensitivity analysis, the performance simulator for ships in actual seas (VESTA) is used, and a comparison is carried out for the fuel consumption calculated from the frequency response of each added resistance in waves. As a result, it is found that the tendency in added resistance in very short waves affects the fuel consumption and the decrease of ship speed.

Исследования особенностей снижения продольной качки и дополнительного сопротивления судна с крыльевыми устройствами

В данной статье на основе предложенного расчета качки судна с энергосберегающими крыльевыми устройствами производится оценка мореходности и ходкости такого судна и возможности целенаправленного уменьшения амплитуд качки и снижения дополнительного сопротивления на волнении. Продольная качка судна заданного типа, обводов и размерений при наличии крыльевых элементов на заданном регулярном волнении рассчитывается с привлечением совместных уравнений вертикально-килевой качки с учетом демпфирования и инерции крыльевых устройств. При этом используется теория Теодорсена колеблющегося профиля и разложение нестационарных коэффициентов подъемной силы и момента по кинематическим параметрам при комбинировании вертикальных и угловых колебаний, и, в общем случае, в условиях воздействия орбитального движения жидкости. Для оценки дополнительного сопротивления используется теория Герритсмы и Бекельмана. В ходе расчетов демонстрируется влияние на дополнительное сопротивление удлинения и площади энергосберегающих крыльев, а также возможности снижения дополнительного сопротивления при совместном использовании носового и кормового крыльев по сравнению со случаем использования только одного (носового или кормового) крыла. Полученные расчетные данные позволяют получить представление о механизме влияния энергосберегающих крыльев на умерение амплитуд качки и снижение дополнительного сопротивления на волнении.In this article on the basis of the method for calculation of longitudinal motions of a ship with energy-saving wing devices proposed there is made an estimation of seaworthiness and seagoing capacity of such a ship and also of a possibility of directed decrease of ship motions amplitudes and added resistance in waves. The longitudinal motions of a ship of a given type, configuration and dimensions, in presence of wing elements, and in given regular waves is calculated with use of coupled equations of heave and pitch motions with account of damping and inertia of wing devices. Used therewith is Theodorsen theory of oscillating foil and expansion of lift and moment coefficients with respect to kinematic parameters for combined heave-and-pitch oscillations and, in general case, subject to action of orbital motion of fluid particles. To estimate added resistance the Beuklman-Gerritsma theory is used. Demonstrated in the course of calculations is the influence of aspect ratio and area of energy-saving wing upon the added resistance as well as upon its decrease when combining use of both bow and stern wings as compared to the case of using just one (bow or stern) wing. Obtained calculated data allow to understand the mechanism of the influence of energy-saving wings upon decrease of the amplitude of ship motions and the added resistance in waves.