A practical method for predicting the propulsive performance of energy efficient ship with wave devouring hydrofoils at actual seas

Abstract

The Energy Efficiency Design Index (EEDI) is made mandatory by the International Maritime Organization to reduce emissions of greenhouse gases from international shipping. In this study, wave energy recovery using a pair of hydrofoils fixed at the ship bow to realize energy efficient propulsion is proposed. This so-called wave devouring hydrofoil (WDH) functions both as an anti-motion fin and a wave energy device, which can help reduce the ship wave added resistance, heave and pitch responses. To evaluate its performance, the coupled interaction between the hydrofoils and the ship under head sea condition is first modeled in the frequency domain together with the evaluation of wave added resistance in the presence of the WDHs. Model test is then conducted using a sample containership. Both the beneficial effect of the WDHs and the validity of the numerical model are proved. The peak response is reduced by 80%, 30% and 25% for added resistance, heave and pitch, respectively. This model is then further modified to include other wave directions. Based on frequency domain results, short-term and long term predictions of speed loss, engine power increase and propeller racing are performed for a 3100TEU containership along her transportation route. The merit of this prediction model is that the hull -propeller -engine interactions is considered from a system balance point of view. It is demonstrated that the WDHs can contribute to the energy-efficient ship propulsion at actual seas, achieving a slight reduction of EEDI and ensuring less speed loss and propeller racing.

A probabilistic method to evaluate bow foils for realistic seas and shipping routes

“…Scientific research has included both experimental (Bockmann and Steen, 2014;Huang et al, 2016) and numerical studies (Belibassakis and Filippas, 2015;Belibassakis and Politis, 2013;De Silva and Yamaguchi, 2012). More specifically, research has focused on a range of aspects including anti-pitching fins on ships (Abkowitz, 1959;Stefun, 1959;Wu et al, 1996), numerical prediction (Bockmann and Steen, 2016;Isshiki and Murakami, 1984), foil pitch mechanism (Bockmann and Steen, 2014;Naito and Isshiki, 2005), size and location (Feng et al, 2014;Naito and Isshiki, 2005), ship coupling (Bowker et al, 2021;Filippas, 2015;Feng et al, 2014), resistance and propulsion (Belibassakis et al, 2021;Feng et al, 2014), oblique waves (Feng et al, 2014) and free surface effects (Filippas et al, 2020).…”

“…Realistic seas refers to the ambient wave energy encountered by a ship for the intended or current shipping route. Previous methods by Naito and Isshiki (2005), Feng et al (2014) and Bockmann et al (2018) have undertaken numerical simulations to calculate the effect of bow foils on ship propulsion and motions in realistic waves. In all cases, strip theory was employed to resolve the ship motions in the frequency domain, which could then be transferred to evaluate the forces acting on the bow foil.…”

“…Combining this with the added resistance in waves, Naito and Isshiki (2005) was able to predict the speed loss in irregular waves for with and without a bow foil. To resolve the effect of bow foils on the ship's engine load and speed, Feng et al (2014) expanded the coupled solution by combining the ship-foil response with propulsive coefficients, then implemented this method to evaluate the effect of bow foils on a ship's engine load for a specific route, accounting for wave statistics. This method was advanced by Bockmann et al (2018) to include the effect of dynamic stall on the foil lift forces for large angles of attack, which was achieved using a hybrid time domain solution.…”

“…A numerical method was presented by Feng et al (2014) to assess the performance of bow foils for a ship route in the North Pacific including wave statistics. This method combines the spectral ship-foil response with the probability of occurrence for a particular sea state, assuming head seas.…”

“…The heading contribution was weighted equally across all directions, resulting in a 1/9 probability of foil effectiveness in head seas (160-180 deg). In order to evaluate the effect of bow foils on the ship's CO 2 emissions in realistic seas, Feng et al (2014) calculated the ship's Energy Efficiency Design Index (EEDI) for with and without foils. Contrastingly, Bockmann et al (2018) implemented a Monte Carlo approach to investigate the effect of bow foils in realistic seas.…”