The Stress Distribution And Computing Of Longitudinal Strength Of Damaged Ships

Damage ship is in a dangerous state, On the one hand the break flooded and liquid outflow will cause the hull of the floating state and the load distribution of a significant change occurs; The other hand, the bearing capacity of the hull structure will be severely weakened.fast and accurate checking of damage the current strengt, is a guide for emergency response and remediation work,So as to reduce casualties and economic losses. The Simple beam theory based on linear elastic theory, the longitudinal bending stress linear distribution at height direction in the cross section, used the average stress at a height of the profile to assess the strength. In the calculation of the full intensity of hulll and the simple beam method is convenient and accurate. Most classification societies are to regulate the introduction of the simple beam method. Longitudinal strength program based on straight beam method is very common. But for the damaged ship carrying capacity in terms of break get down, the regional component is a dangerous area. Break the stress concentration, break the plastic, as well as other issues such as tear break straight beam method can not be resolved.Use the average stress calculated by simple beam to evaluate the longitudinal strength of damaged ship hulls and ignore the strength of breaks,the treatment is crude and unreasonable. FEA is a effective means to study the break stress concentration and structure nonlinear problems. The break stress concentration is localized, the area far away from the break had little effect, So can take the stress calculated by the simple beam of full profile bottom in the same boat load as the nominal stress, combined with FEA to study the stress concentration.of break at the bottom..The content and results of this study are as follows:1) stduy the mesh and the selection the location of observation point for the stress concentration, for the three typica breaks rectangular, rectangular with sharp corners, circle in the bottom stiffened plate. To provide a reference for mesh of breaks in the stiffened plate of the damage ship for others stduy.2) Breaks in the stiffened plate is different from break in flat, in addition to its own break by the impact of the shape and size but also by the aggregate impact of foreign. Use "crossing method" let the break cross vertical, lateral in the bottom stiffened plate, To study the relationship between the stress of the break and longitudinal. Using this rule can be obtained given the maximum and minimum stress in the bottom break, determine the break of the most dangerous situation.3) Study Variation of SCF of breaks three typical long the bottom of the boat break vertical and horizontal extensions by FEA. In order to facilitate analysis, the SCF of breaks is divided into the flat SCF and the Aggregate interaction coefficients. The results showed that:difference of tress concentration factor curveof rectangular and rectangular with sharp corners, circle was similar to a gradual increase relationship. Therefore, the unknown break stress concentration factor can be calculated by few stress concentration factors had konwned by the relationship. And the example shows that the algorithm is feasible. Change the longitudinal distance in the case, there are also the law that the law of the stiffened panel format with general versatility.4) Study the stress concentration on the break nonlinear FEA, gradually by increasing the load to break into the plastic stage. Comparison the plastic stage of the stress concentration factor with the linear stress concentration factor. A wide range of break sizes calculated,to sum up the modified formula for stress concentration of the plastic stage.5) Calculate the average stress at the same height of profile by simple beam theory,with the stiffened plate break stress concentration factor in the expansion of the law of grid, This paper presents a calculation of such damage until the hull girder longitudinal strength of the correction method. Makes the total longitudinal strength of hull damage assessment is more accurate. And validated with an example, the results show that the correction method is feasible and suitable for programming.