Development of a heat transfer analysis program by an efficient and simplified numerical technique: Application to LNGC

Heat transfer analysis in ships handling LNG as cargo or fuel at extremely low temperatures has two purposes, i.e., 1) to select steel grades based on temperature distribution to protect the hull structure from extremely low-temperature cargo and 2) to obtain the boil-off rate (BOR) by calculating the amount of heat flowing into the cargo hold. For a typical LNG carrier (LNGC), the heat transfer model can be simplified by introducing the overall heat transfer coefficient, which enables easy and fast heat transfer analysis. However, as various ships and containers for transporting and storing cryogenic cargoes or fuels such as LNG were developed, a heat transfer analysis program that could be applied to various and complex shapes became necessary. Methods and programs considering various hull structures and complex shapes have been proposed and developed. The concept of the finite element method was introduced to consider various shapes in heat transfer analysis. The hull and surrounding space are divided into panels and spaces, and heat transfer problems can be solved in 2D or 3D by defining line, plane, and volume elements. The basic heat transfer equations were derived by defining a unit heat transfer model consisting of one panel and two spaces and a unit heat balance model consisting of one space and multiple panels. The heat transfer equations of the unit models were assembled into the equations of the entire model, and the equations were solved using matrix operations. Heat transfer analysis for LNG ships was performed using the developed program to calculate temperature distribution and BOR. Analysis models for various types of LNG ships were created to verify the applicability and usability of the program. Additionally, we reviewed issues that may be considered in the heat transfer analysis of ships.