THE INFLUENCE OF LOCAL RESIDUAL DEFORMATIONS ON THE SHIPS HULLS RELIABILITY

Abstract

The changes in the bearing capacity of the hull sheets and beams of the ship’s set under the action of compressive and tensile forces are studied in the paper. The inf luence of local residual deformations on the permissible wear of the deformed element, which allows assessing its reliability, is established. Since the longitudinal forces (compressive and tensile) are significant only for the deck or bottom in the middle part of the hull, the effect of local residual deformations on the bearing capacity of sheets and beams of the longitudinal set is estimated only for these elements. It is assumed that the retained local residual deformations of the housing elements do not change with the time of ship operation. Corrections for permissible wear in the cross-section equal to a decrease in the average thickness of the sheets in the cross-section are calculated (for a section of the body equal to the length of the sheet, from joint to joint). The wear rate of all cross-section sheets is assumed to be the same, and the probability of its occurrence corresponds to the law of normal distribution with the characteristics specified in the Rules of the Russian River Register established for a given group of elements. According to the assumptions made above, it is possible to calculate the probability of failure in the cross-section of a group of elements with local residual deformations depending on the number of years of the vessel operation. The probability of failures in a given group of elements is estimated by the multiplication of the failures probability in several sections after a given number of years of operation. The probability of failures in the hull of the vessel is calculated as the multiplication of the failures probabilities in all groups of elements. Formulas for calculating the loss of the bearing area of the sheathing plates and beams of the longitudinal set due to the local residual deformations have been obtained. The loss of the working area of the sheets and longitudinal beams is represented as additional wear of the sheets. After dividing the mentioned loss of the cross-section area by the cross-section width, the value of the permissible reduction in the residual thickness of the sheets, weighted average for the section under consideration, is obtained.