Stress Assessment Of Wake Equalizing Duct Design For VLCC

With fuel prices increased, a growing number of energy-saving devices are being used to improve merchant propeller efficiency and reduce fuel consumption. Wake equalizing duct is currently the most widely used new creation as a merchant energy-saving devices for its simple structure, easy installation, high energy-saving effect and other characteristics. But the damage occurred at the junction between hull structural and wake equalizing duct sometimes, especially with the development of large ships, the size of duct accordingly becomes huge, accompanied by structural strength, vibration problems have become increasingly prominent.The requirement by the classification societies in the world for the wake equalizing duct structure design verification is still blank. Japan and South Korea and other countries had deep study on energy-saving devices such as wake equalizing duct structure, but kept secret. Domestic engineers have analyzed the performance of the vibration before, but few studies assess the structural strength. Therefore, the study in structural strength as the large size of wake equalizing duct is very important to promote the widespread use of large-scale energy-saving devices and to improve the economics and safety of large vessels.In this paper, by using of the very large crude oil tankers (VLCC) as the carrier, the research method is studied, and a safe and reliable structure of wake equalizing duct is designed.As the wake equalizing duct being affected by the propeller exciting forces, and the stern flow field is very complex, the wake equalizing duct will be dangerous in vibration. If not properly designed, the causing resonance will produce structural damage or even destroy the propeller. This article makes an assessment on the resonance risk for the wake equalizing duct. By using of the finite element method and boundary element method to get the natural frequencies and mode shapes of the wake equalizing duct in air and water, different strengthening methods are compared and analyzed, and ultimately determine the appropriate wake equalizing duct structure design.According to IACS Common Structural Rules (CSR) and Germanischer Lloyd (GL RULES) in the hull load requirements, the load of wake equalizing duct structure in the actual operations is analyzed. These loads include the three-way movement of the hull caused by the inertial force, different hydrodynamic waves, wave-slamming load by pitching, and the lateral force by cross-flow under the action of. By the establishment of three-dimensional finite element model of the wake equalizing duct according to the different load combinations, structural finite element analysis of stress levels are checked. By using simple mechanical model to investigate the wake equalizing duct structure design methods and estimation formula verified by finite element analysis, the results are satisfactory, indicating that the method for solving practical engineering problems have a certain reference value.