How safe is 'safe'? Ship dynamics in critical sea states

How safe is 'safe'? During the design phase of floating structures, specifications such as range of application, warranty of economical efficiency and reliability are integral parts of the evaluation process. The key decision is the choice of environmental design conditions to be considered for operation and survival: this issue cannot be solved globally, i.e. different operating conditions (transit, operation, survival) and criteria (body motions, local and global loads) will lead to individual results. In this paper a procedure for the systematic identification of critical (design) wave sequences for offshore structures is presented-a response based identification tool for critical wave sequence detection. The basic principle of this procedure is characterized by tailoring of short wave sequences to obtain a certain maximum response. The fully automated procedure combines wave/structure interaction analysis programs with an optimization algorithm. The objective is to find a critical wave sequence with respect to the predefined maximum responses. By means of this procedure, the identification and evaluation of critical design conditions can be conducted more systematically, accurately and thus efficiently. To demonstrate the broad scope of this procedure, a typical example is presented. The results obtained are reviewed against classical design methods. The investigations comprise numerical calculations as well as model test validations.