In order to study the variation law of the resistance of the trim drag reduction to the fat and shallow draft type such as inland vessel, this paper takes a 2000t bulk carrier as the research ship. The optimization effect of trim adjustment on this type of ship is verified by the method of combining model test and numerical calculation. The drag reduction efficiency of the ship at the ballast and design draft is displayed through the resistance change curve, pressure distribution diagram and wave height diagram, and the optimal trim curve at a certain speed is obtained.
Energy conservation and emission reduction of ships has become a common issue around the world. According to the latest meeting requirements of the Marine Environmental Protection Committee of the International Maritime Organization, from 2023, stricter technical and operational monitoring of greenhouse gas emissions from ships on international voyages will be carried out. In recent years, with the implementation of IMO's "2020 Sulfur Restriction Order", in order to meet the requirements, most shipping companies choose to let their ships use higher-priced low-sulfur fuel oil, which increases operating costs (Ai and Zhu, 2022).
When it comes to green shipping, one of the main concerns about ship hydrodynamics is resistance reduction (Lyu, Tu, Xie and Song, 2018). From a practical point of view, ship energy conservation and emission reduction is to improve the energy utilization and transportation efficiency of ships; reduce energy consumption, and use less energy consumption to achieve efficient transportation of ships (Lv, 2020). At present, the application of energy-saving and emission-reduction technology mainly includes four aspects: the use of economical speed, the reduction of drag and consumption by the hull, the improvement of the propulsion efficiency of ships, and the recovery of waste heat and waste gas of ships. Taking a single voyage of a ship as the research object, based on historical data, Li (2021) calculated the CO2 emissions and voyage benefits of the ship at different speeds. The calculation results show that the ship operates at a speed of 10 knots to 11 knots, which can maintain a relatively high speed and profitable status, but also to achieve a lower level of CO2 emissions from ships. However, this method of finding the best balance point of ship's speed and fuel consumption related calculation formula is not suitable for all ships. During the LNG ship's transportation, the cargo tank is dynamically generating boil-off gas at all times, so it must be precisely controlled (Song, 2021). Improving the recommended efficiency of ships refers to installing energy-saving devices such as fairing fins and rudder balls at the stern of the ship to make the propeller flow evenly. Nevertheless, the energy-saving effect varies with different ship types and energy-saving devices. In general, the energy-saving efficiency can reach 2% to 8% (Zhang, Zhao and Wang, 2016). Luo (2021) investigated the effect of the heat exchanger water flow rate on the exhaust gas waste heat utilization rate and the heat exchanger exhaust gas outlet temperature. The results show that, the maximum hear recovery is 112.73kW, and the average waste heat recovery rate can reach 67.65%. Although the water flow control of the exhaust heat recovery system has strong practical value, this system is only suitable for ships powered by diesel. At present, many ships have begun to use gas/oil dual-fuel propulsion systems and more energy-saving sources, so the practical application range of this method is not extensive.