Research On Key Issues Of Ship Traffic Safety Goal Determination In Safety Level Approach

The scientificity of ship traffic safety goals in safety level approach has a direct influence on the rationality,the availability and the credibility of the maritime rule compliance verification.In order to avoide setting safety goals too high or too low,the research on key issues involved in setting ship traffic safety goals is necessary.Such issues include the time window selection in the ship traffic accident statistics,the uncertainty quantification of the risk analysis result in formal safety assessment and the establishment of the societal risk criteria.In order to grasp the risk trend for setting ship traffic safety goals,the time window selection model in the ship traffic accident statistics is proposed.In the model,the uncertain time series of ship traffic accident probabilities is established based on the trend analysis of ship traffic accident probabilities.Then the sliding window method is used to implement the segmentation of the uncertain time series,which aggregates the relatively concentrative confidence interval of each time stamp.According to the orderliness and the continuity of time series,the closest segmentation to the current time is selected as the statistical time window.The United Kingdom's ship traffic and the,international cruise ship traffic accident data are used for case study.In addition,related simplifications in the model are discussed.Based on the comparison with the past time window selection method,the effectiveness of the proposed model is validated.For the determination of ship traffic safety goals in safety level approach,the actual ship traffic risk level can be provided by the risk analysis result in formal safety assessment.According to the formal safety assessment research which is carried out,the method for quantifying the uncertainty of the risk analysis result in formal safety assessment is proposed.Based on the uncertainty identification and classification of the risk analysis process in the formal safety assessment,the method uses the probability distribution and the possibility distribution to model and propagate the aleatory and epistemic uncertainties,which are eventually represented in two dimensions.A case study is carried out to the cruise ship traffic,and the effectiveness of the proposed method is validated by the comparison with the uncertainty quantification method based on the possibility theory.The acceptability evaluation of the actual ship traffic risk level is necessary when ship traffic safety goals are determined by the actual ship traffic risk level.Based on the consistency with individual risk criteria and the principle of continuous improvement,which is frequently used in the process of setting safety goals,an approach to establish the societal risk criteria is proposed.The approach is suitable for the process of determining ship traffic safety goals.Furthermore,by defining dynamic coefficients to express the risk aversion,a method for the acceptability evaluation of the societal risk is developed based on the established societal risk criteria.Finally,a case study is carried out to the cruise ship traffic and the ro-ro passenger ship traffic.According to the comparison with the societal risk criteria developed by the International Maritime Organization,the effectiveness of the proposed establishment approach and evaluation method are validated.According to the analysis of principles and approaches for setting safety goals in the past,the method for setting ship traffic safety goals in safety level approach is proposed.The method is based on the actual ship traffic risk level and the effects of the variation trend,the uncertainty and the acceptability of the actual ship traffic risk level are considered.In addition,opinions of stakeholders are also considered in the method.A case study is carried out to the cruise ship traffic,and the effectiveness of the proposed method is validated based on the comparison with the ship traffic safety goals calculated by the actual risk method.The research on key issues involved in the process of determining ship traffic safety goals is conducted and methods are proposed.Based on the actual ship traffic accident data,the effectiveness of the proposed methods is validated by the comparison with the past research methods,and the proposed methods are more suitable for the process of determining ship traffic safety goals.The research helps speed up the study process of safety level approach and provides basis for the function requirement quantification and the compliance verification of maritime rules.