船舶应急抛锚计算方法研究

Research on Calculation Method of Emergency Anchoring

应用常规经验公式和有限元CEL大变形计算方法,结合抛锚试验,研究了上海LNG管道项目北港5 wt级船舶8.3 t船锚、南港40 wt级船舶18.80 t船锚在BSZ111等多个钻孔点的应急抛锚贯入深度情况,其中CEL方法还考虑了正面贯入、窄面斜向贯入和宽面斜向贯入情况.公式法计算的应急抛锚最大贯入深度北港为2.60m,南港为3.13 m,而有限元CEL大变形计算方法得出北港为2.86 m,南港为5.24 m.结果表明:CEL方法计算所得窄边(60°)贯入深度普遍大于经验公式计算所得值,说明横截面积的变化是影响贯入深度计算的重要因素.公式法的结果受到土壤系数恒定不变因素的限制,无法考虑贯入过程中土壤的竖向和横向刚度的变化,结果相对偏小,而CEL法可考虑多层土壤刚度以及土壤刚度随土层变形增加后的折减,计算过程更为客观,结果偏于安全考虑,适合作为设计依据.所以,对土层组成相对单一时可采用公式法,而对土层组成多变的复杂情况,建议采用更加客观和安全的CEL方法.

The emergency anchoring penetration depths of 8.3 t anchor of 5 wt class ship in North Port and 18.80 t anchor of 40 wt class ship in South Port of Shanghai LNG Pipeline Project at BSZ111 and other drilling points are studied by using the conventional empirical formula and finite element CEL large deformation calculation method,combined with anchoring tests.The CEL method also considers frontal penetration,narrow oblique penetration and wide oblique penetration.The maximum penetration depth of emergency anchoring calculated by the formula method is 2.60 M in North Port and 3.13 M in South Port,while that calculated by finite element CEL large deformation calculation method is 2.86 m in North Port and 5.24 m in South Port.The results show that the penetration depth of the narrow edge(60 degrees)calculated by CEL method is generally larger than that calculated by empirical formula,indicating that the change of cross-sectional area is an important factor affecting the calculation of penetration depth.The results of the formula method are limited by the constant and invariable factors of soil coefficient.It is impossible to consider the changes of vertical and transverse stiffness of soil during penetration.The results are relatively small.The CEL method can consider the multi-layer soil stiffness and the reduction of soil stiffness with the soil deformation.The calculation process is more objective,and the results are in favor of safety considerations,which is suitable for design basis.Therefore,when the composition of the soil layer is relatively single,the formula method can be used,while for the complex situation of the varying composition of the stratum,the more objective and safe CEL method is suggested.