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.

UNCERTAINTY ANALYSIS OF SHIP MODEL RESISTANCE TEST IN ACTUAL SEAS

Resistance test is a classical method used to study ship performance. In this study, the uncertainty of large-scale ship model resistance test in actual seas is analyzed. Considering the difference between these trials and traditional test in towing tanks, this study first uses the ITTC 2014 procedure based on GUM to calculate the systematic error in the test. The parameters that affect the test accuracy are also estimated. Then, the program based on the Monte Carlo method is verified, and the differences between the two methods are compared. In this study, the uncertainty sources in the test are quantitatively analyzed, and the results will be helpful for improving the ship model test scheme in actual seas.

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.

Numerical Simulation of Drifting and Run-Up Ice Floes Driven by Tsunami

In order to simulate drifting and run-up ice floes driven by tsunamis, we developed a quasi-3D Discrete Element Method (DEM) in which phenomena unique to granular solids, such as the arch action, jam and pile up of such solids, can be simulated with a small computation load. The validity of the simulation method was verified by hydraulic experiments using synthetic ice. Some numerical simulations of drifting and run-up ice floes driven by a tsunami were performed to investigate the fundamental characteristics of ice run-up and the applicability to actual seas. It was confirmed that the simulation results could estimate risk areas where ice pile up and jam form as well as hazardous areas showing the degree of damage to buildings. Such calculation was expected to be useful for the compilation of hazard maps and the development of disaster mitigation plans in the future.