No abstract

The assessment of the residual strength of a damaged ship is a key element of ABS’ Rapid Response Damage Assessment (RRDA) program. When determining the residual strength, it is important to understand how the initial structural damage can spread in response to sea wave dynamic loads and can lead to a gradual reduction of the ship’s residual strength. This progressive, time-dependent structural failure caused by cracks emanating from the damaged area could eventually lead to total hull girder collapse. This is why it is important to quantify the progressive structural failure over time when assessing the residual strength of the damaged ship. Until now, progressive structural failure analysis has been conducted numerically using the Finite Element (FE) modeling approach. While this approach is accurate, it is extremely time-consuming, which makes it inappropriate for incident response, where time for decision-making is very limited. In order to overcome this limitation, an alternative analytical modeling approach for assessing the progressive structural failure of a damaged ship is proposed. This paper presents a new comprehensive procedure for analytical prediction of crack propagation under sea wave loading using spectral fatigue analysis, beam theory, fracture mechanics and an equivalent stress intensity factor (SIF) range concept. The SIF range obtained analytically is validated by FE modeling of a damaged ship subjected to sea wave dynamic loading. The procedure for analytical prediction of the crack propagation is demonstrated for a typical, modern 170,000 DWT bulk carrier in a full load condition. The results of this research can be used to support informed decision-making when analyzing a vessel’s residual strength for the transit voyage from the accident location to a repair facility.

Numerical and experimental simulations for residual strength analysis of ship structures have recently been investigated in the marine industry. The technology of residual strength analysis is mature enough to assist ocean-going vessels shortly after experiencing a damage incident. The analysis can be used to evaluate the remedial actions necessary to minimize the risk of further damage during stabilization efforts and allow for the eventual transit to a repair facility. In 2010, the American Bureau of Shipping (ABS) implemented enhancements to its Rapid Response Damage Assessment (RRDA) program, in particular to the evaluation of residual strength. An integrated software system was developed to quickly and efficiently provide guidance to the ship owner through the utilization of the analysis results. This paper highlights the residual strength analysis results of several actual RRDA cases evaluated in recent years. These results were obtained from the application of an analysis software system, which includes the ability to perform timely calculations of the hull girder ultimate strength, hull girder shear stress, buckling and local strength in the damaged condition. This paper also provides an example of the use of analysis data to provide recommendations for remedial actions during a response. The strengths and weaknesses of this current analysis procedure are discussed and conclusions about the use of this software tool in damage scenarios are evaluated by comparing the analysis results with the outcomes of the presented cases.