船舶与海洋工程制造工艺力学理论及工程应用(英文版)

Chapter 1 Introduction The construction of naval architectures and marine structures is a complicated fabrication process involving cutting， plate bending， and assembling through thermal procedures. To enhance the fabrication accuracy and market competition， it is desired to optimize the processing parameters during thermal fabrication of shipbuilding through investigation of processing mechanics and clarification of mechanical response. Based on mechanical theory， processing mechanics with thermal procedures focuses on the mechanical response during fabrication to improve the construction level of ship structures and optimize processing parameters. Thermal fabrication procedures such as cutting with oxygen， plate bending with natural gas， and arc welding constitute critical research issues given that they play important roles during the ship construction and all of them undergo non-linear thermal-elastic-plastic response. To address the thermal-elastic-plastic problem during the application of thermal fabrication procedures， finite element (FE) analysis is usually employed to obtain numerical solutions by considering processing conditions as thermal loading， as well as thermal and mechanical boundary conditions during computation. Therefore， it is useful and helpful to understand the generation mechanism of residual stress and distortion during the application of thermal fabrication procedures through mathematical modeling and FE computation. Currently， the processing parameters can also be assessed before actual ship construction. Moreover， an optimized fabrication plan can be considered to avoid the engineering problems of stress concentration and dimensional accuracy and to enhance the manufacturing quality significantly. 1.1 Research Background With the rapid development of the world economy， there is an increasing demand for energy. The development of the seabed oil field all over the world has expanded from shallow sea to deep sea and even ice-sea areas. Consequently， the material and technical requirements for manufacturing of offshore platforms steadily grow， especially those of offshore drilling jack-up platform legs， which have already been constructed by z-direction steel with yield strength over 690 MPa and maximum thickness of 210 mm [1]. Cutting a high-strength and large-thickness rack is a complex thermal processing procedure involving heat transfer， material metallurgy， solid and fluid mechanics， and several other sciences， in addition to the complex interaction between materials and cutting gas. After cutting， the shrinkage stress is produced with the natural cooling down of the steel plate. Notable complex deformation may also be produced. As the first processing procedure of welding production， cutting efficiency and quality directly influence the welding deformation of the entire structure. The neglect of the residual stress and strain in turn influence the resulting welding quality and reduce the structure strength， with an underlying hidden danger of crack expansion. Flame cutting is a common method for plate cutting. However， dry carbides are energy-consuming， and the storage and use of acetylene are potentially hazardous. Given that the cutting process has numerous thermal-impact factors such as residual stress and deformation， cutting a large high-strength thickness plate for an offshore jack-up platform leg rack should be previously examined. Oxygen cutting is more complex. The cutting process will produce a non-uniform temperature field and will be accompanied by thermal strain and partial plastic deformation. Currently， there is no reference related to this area. Thus， thermodynamic behavior research on cutting large high-strength thickness racks demand a great deal of experiments to provide theoretical and technical support for the improvement of the construction process， which plays an important theoretical research role and has engineering application value. After applying a cutting procedure， plate bending is usually employed for curveplate processing during the construction of modern ship and offshore structures. The ship hull is made up of a large number of plates with complex curvatures， especially at the bow and stern， where many double-curvature plates such as saddle or sail shapes are located. Thus， plate formation is an essential procedure for shipbuilding， which will be related to the production efficiency and precision of the ship structure， as well as to the fabrication cost and schedule of shipyards [2]. Hot formation is an important method of plate bending in shipyards. The temperature distribution in the thickness direction is uneven because of local plate heating. Hence， a bending moment would be generated for the plate to produce out-of-plane displacement. There are three main procedures of hot formation according to the applied heating source， namely line heating with flame (oxygen-acetylene flame)， laser heating， and high-freque