Study on competition mechanism of deformation modes of U-shaped bellows under internal pressure

Bellows are widely used in various modern engineering fields, especially in storage and transportation of floating liquefied natural gas (FLNG) system on the sea. They are prominent pressure vessels with internal pressure load as a common working condition. Concerning common U-shaped bellows in this study, the cross-section of the bellows is divided into three segments, wave peak semicircle, straight ring plate, and wave trough semicircle, to establish mechanical models. Bellows with different design parameters have different mechanical properties, producing different deformation modes of the cross-section of the bellows under the action of internal pressure load. The competition mechanism of deformation modes of different parts in the cross-section under internal pressure is discussed. Furthermore, the sensitivity analysis of design parameters is performed and the bellows with competition balance between different parts were determined, which can keep the cross-section maintaining the “U” shape without global deformation under internal pressure. In addition, the radial displacement of bellows under internal pressure is theoretically derived to improve the deep discussion on competition mechanism of deformation modes. Accordingly, the relevant theoretical results are compared with finite element simulations, illustrating the reliability of the theoretical analysis. This study may serve as a reference for the design and analysis of the structure of bellows.