Numerical Simulation of Thrust Deduction Factor and Hull Form Optimization for Propulsive Efficiency of Large Containership and Bulk Carrier
Date Issued
2015
Date
2015
Author(s)
Lin, Tsung-Yueh
Abstract
Based on the flow characteristics in ship propulsion, the interaction between ship hull and propeller is assumed to be inviscid in nature. A boundary element method (BEM) with circulation present is employed to solve the Laplace equation for the augmented resistance of the hull. The governing equation for wake interaction is built upon the stream surface contraction caused by the propeller’s induced velocity. According to the Lagally theorem, thrust deduction scaling originates from the scaling of the effective wake. The former is a potential-based interaction, while the latter is based on a viscous boundary layer basis. The scale correction of the thrust deduction factor works with the proposed balanced self-propulsion test procedure without using a skin friction corrector. An implementation of the self-propulsion framework integrates computational fluid dynamics method (CFD) and BEM methods but decouples the hull-propeller interaction solvers from them. This approach drastically reduces computation time, such that a propulsion simulation may be completed within minutes. The framework is validated for a moderate speed containership, and further extended by the lifting line method for faster hull performance analysis. On the hull form design aspect, challenges of high efficiency ship designs have attracted much attention due to the requirement for reduction in NOx emission. Optimizations for the propulsive efficiency are feasible by utilizing the decoupled approach of propulsion simulation, and many combinatorial options from hull forms and propellers are accomplished without suffering long simulation times in CFD. A parametric hull form transformation model, based on the cubic Bezier curve formulation to keep displacement constant, is proposed. Thirty hull forms of five sectional area curve patterns are studied and an optimal set is found. Compromises between resistance, hull efficiency, and propeller efficiency exist along the optimal frontier, on which a design principle is derived. According to this principle, a successful modification of the tanker brings a reduction in delivered horse power by 17.3% due to a 23.7% decrease in thrust deduction, but with paying a price of a 3.2% increase in its towed resistance.
Subjects
Thrust Deduction
Hull Efficiency
Propulsion Simulation
Hull Form Optimization
CFD
Type
thesis
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