Session: 02-04-01 Fatigue and Fracture Reliability 1

Paper Number: 80212

80212 - Research on Fatigue Load Analysis and Fatigue Strength Assessment of Stern Shaft Bracket of Large Ship 

The stern shaft bracket of a ship is a bracket supporting the propulsion shaft outside the ship. With the gradual enlargement of tonnage and improvement of performance in ship industry, the structural safety of stern shaft bracket should raise more and more concern. At present, the research on the fatigue strength characteristic of stern shaft bracket is almost in worldwide blank. Taking a large ship as an example, the fatigue loads and structural fatigue strength of the stern shaft bracket were studied in this paper. The main research contents included the following aspects:

1. In this paper, three kinds of external loads causing fatigue damage of stern shaft bracket were analyzed, respectively were: propeller excitation force, wave load and local fatigue hydrodynamic force. The computational formula of local fatigue hydrodynamic force was derived, and the computational fluid mechanics software “Fluent” was adopted for auxiliary calculation.

2. This paper studied the fatigue damage of stern shaft bracket separately under the action of high-frequency load (propeller excitation force) or low-frequency load (wave load and local fatigue hydrodynamic force):

1) Empirical formulas were used to calculate the propeller excitation force. Dynamic analysis of stern shaft bracket was carried out by using the finite element software Patran to obtain the stress time history, through which the fatigue damage of stern shaft bracket under the action of  propeller excitation force could be calculated;

2) The time-domain calculation method for the fatigue damage of stern shaft bracket under low-frequency load was studied. The method and procedures of obtaining the stress time history of the stern shaft bracket under the combined action of wave load and local fatigue hydrodynamic force under the irregular wave were systematically studied and described in detail.

3) Based on the rain-flow counting method and the linear cumulative damage theory, the fatigue damage under the combined action of the two low-frequency loads was calculated. According to the fatigue research in this paper, an effective calculation method for fatigue assessment of stern shaft bracket was presented.

Keywords: Stern shaft bracket; Propeller excitation force; Wave load; Local hydrodynamic; Fatigue strength analysis; Time domain method

Presenting Author: CHEN XIANYIN Marine Design & Research Institute of China

Authors:

CHEN XIANYIN Marine Design & Research Institute of China
Wang Gaoxiang China Construction Steel Structure Corp, LTD
Zhu Qingchun Marine Design & Research Institute of China