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This study focussed on the mooring positioning of a jack-up platform. A numerical analysis was performed using ANSYS to examine the performance of a mooring system in time and frequency domains. The hydrodynamic response of the platform was analysed, and response amplitude operators were obtained in the frequency domain. A coupling analysis of platform motion was performed in the time domain, which examined the effects of environmental loading directions on platform displacements and the influence of mooring line parameters on mooring positioning performance. The primary concern was effects of the incident angle of environmental load on six components of platform displacement and mooring line tension. Moreover, a multi-objective optimisation technique was employed to control the length and tension of the mooring line in towing and positioning, which can determine the optimal length of the mooring line and then assist in achieving accurate platform positioning and steady mooring. [ABSTRACT FROM AUTHOR]

This study focused on the buckling of stainless steel spherical caps under uniform external pressure. Caps with a circular arc meridian have a nominal base diameter of 146 mm, nominal uniform wall thickness of 1 mm and nominal height of 37 mm. Six nominally identical laboratory-scale caps were fabricated, measured precisely and tested slowly. The buckling performances of such caps were studied experimentally and numerically, and the results show good agreement with each other. Furthermore, the buckling of 13 mass-equivalent caps of various heights were numerically analysed to identify the cap with the best load-carrying capacity. The results suggest that a spherical cap with height-to-base diameter ratio of 0.274 supports the highest buckling load. Such a cap can be applied as an end-closure for cylindrical pressure hulls or as a manhole cover for manned cabins in deep-sea vehicles. [ABSTRACT FROM AUTHOR]

This paper focuses on spherical shells under uniform external pressure. Ten laboratory scale models, each with a nominal diameter of 150 mm, were tested. Half of them were manufactured from a 0.4-mm stainless steel sheet, whereas the remaining five shells were manufactured from a 0.7-mm sheet. The geometry, wall thickness, buckling load, and final collapsed mode of each spherical shell were measured, as well as the material properties of the corresponding sheet. The buckling behaviors of these shells were demonstrated analytically and numerically according to experimental data. Analyses involved considering the average geometry, average wall thicknesses, and average elastic material properties. Numerical calculations entailed considering the true geometry, average wall thicknesses, and elastic-plastic modeling of true stress–strain curves. Moreover, the effects of purely elastic and elastic-perfectly plastic models on the buckling loads of spherical shells were examined numerically. The results of the experimental, analytical, and numerical investigations were compared in tables and figures. [ABSTRACT FROM AUTHOR]

This study investigated the buckling performances of stainless steel toroidal shell segments under uniform external pressure. The toroidal shell segments used in this study exhibited a nominal section radius of 70.5 mm, nominal wall thickness of 1.346 mm, and nominal rotation radius of 138 mm. A total of 12 toroidal shell segments were manufactured using roll bending and were measured geometrically, tested hydrostatically, and evaluated numerically. Six of the shell segments had a 45° rotation angle, whereas the other six had a 90° rotation angle. Moreover, the buckling of geometrically perfect toroidal shell segments was explored under various rotation angles ranging from 30° to 360°. • Twelve steel toroidal shell segments were machined via roll bending of male and female dies. • All machined toroidal shell segments were studied experimentally and evaluated numerically. • The effects of toroidal shell segment completeness on the buckling were explored numerically. • Currently used empiric guidelines yield a very conservative assessment for small angle segments. [ABSTRACT FROM AUTHOR]

This study examines the effect of shape index on the elastic buckling of Cassini oval shells under uniform external pressure. Shells are evaluated under a uniform wall thickness (2 mm) and capacity ( 3.63 × 10 6 mm 3 ), with the shape index, k c = c / a , ranging from 0 to 0.99. Several numerical computations, involving linear elastic bifurcation analysis and geometrically nonlinear elastic analysis including eigenmode imperfections, are conducted for these shells. Some of them are investigated experimentally. The results show that a Cassini oval shell with a stable character seems to be an unfavorable shape due to its low load-carrying capacity, which is at variance with previous findings regarding this problem. Notably, the k c = 0.1 Cassini oval geometry, exhibiting a high load-carrying capacity, appears to be a favorable shape in various fields such as underwater tanks, pressure hulls, and artificial capsules. [ABSTRACT FROM AUTHOR]

The subject of the present paper is a family of egg-shaped shells. The meridian of these shells resembles that of a goose egg. The capacity and mass of the shell were maintained constant. The ratio of the minor B to the major L axis of the shell was determined according to the experimental results of the analysis of 333 goose eggs. Fourteen B / L ratios were determined as follows: 0.4, 0.5, 0.6, 0.65, 0.66, 0.67, 0.68, 0.69, 0.70, 0.71, 0.72, 0.8, 0.9 and 1.0. The effect of the ratio on the buckling behavior of the egg-shaped shell was numerically and analytically analyzed. [ABSTRACT FROM AUTHOR]

Spherical shells are presently the most extensively used shapes for pressure hulls in the deep manned submersible. However, it is known that the spherical pressure hull has disadvantages of difficult interior arrangement/low space efficiency, and is highly sensitive to geometric imperfections. These limitations have prevented further developments of the deep manned submersible to some extent. In order to overcome these limitations, two egg-shaped pressure hulls respectively with the constant and variable thickness are proposed in this paper, where the equivalent spherical pressure hull is also presented for comparison. Buckling of these pressure hulls with geometric imperfections are further studied using numerical analyses at a given design load. It is found that, with respect to hull strength, buoyancy reserve, and space efficiency etc., egg-shaped pressure hulls could be optimally coordinated, which appear to be leading to overall better performance than the spherical pressure hull. Especially, the egg-shaped pressure hull is quite less sensitive to the geometric imperfections, making it more convenient and low costly to form the hull in manufacturing or to open holes in applications. It is anticipated that egg-shaped pressure hulls will play a key role in the future development of deep-sea manned submersibles. [ABSTRACT FROM AUTHOR]

This study focused on the buckling of corroded spherical shells with wall-thickness reduction in local regions under a uniform external pressure. For spherical shells whose wall thickness was reduced owing to local corrosion on the outer surface, the effects of the shape, area, depth, and location of the reduction on the buckling properties were evaluated to identify the most dangerous case. Accordingly, the load-carrying capacity of corroded spherical shells with local reduction was predicted. Moreover, by verifying the five buckling prediction formulas of the spherical shells, reasonable prediction formulas for the compressive capacity of the spherical shells under the condition of corrosion defects were obtained. Four scale models were fabricated using resin material for testing. The geometric shape and wall thickness of each spherical shell model were measured and compared with those of the ideal model. Then, the buckling load and ultimate collapse mode were determined through a hydrostatic test. The experimental and numerical analysis results were compared to verify the numerical analysis. • Proposed a formula for predicting the compressive load of a corroded spherical shell. • The effects of the shape, area, depth and location of corrosion thinned on the buckling of the opening spherical shell was discussed. • Taking thickness as local corrosion defects, the nonlinear buckling of the opening spherical shells was discussed. • The numerical results of thinned spherical shells agree well with experimental results. [ABSTRACT FROM AUTHOR]