散裝船擱淺之臨界情節分析

Critical Scenarios Analyses of a Bulk Carrier in the Event of Grounding

This study deals with the ship grounding mechanics applied to a bulk carrier. The ship with a forward speed runs aground by the bow on a shoal. In view of the bow crushing damage, a critical situation is met when the collision bulkhead in way of the keel starts being in contact with the seabed. Critical grounding scenarios are determined by a ship grounds on a seabed with a critical initial forward speed till rest while the structural damage does not exceed the critical situation. First, a mathematical model is proposed 10 analyze the ship grounding and extract the critical initial forward speed. The grounding process can bc divided into two phases. The first phase represents the ship change of momentum, and the second phase is the bow sliding over the seabed. During those two phases, the kinetic energy of the ship is dissipated by friction with the seabed, bow structure plastic crushing and trim increase due to the lift of the bow. Then, the mathematical model is modified based on a few time-consuming ship grounding nonlinear FEAs. This modified mathematical model allows fast and versatile analyses of ship grounding. Finally, critical grounding scenarios including ship critical initial forward speed are estimated. The hull girder strength is also reviewed under critical scenarios. The results show that the hull girder strength is sufficient despite the lift of bow and the flooding caused by localized damages. 本文研究一艘前進中的散裝船船艏擱淺於海床上之力學特性。從船艏壓潰損傷來看，當防碰艙壁與船底龍骨板交接處接觸到海床時，將之視為達到臨界狀態。當船舶以一臨界前進初速度前進擱淺於海床，靜止後若結構損傷範圍不超過此臨界狀態，即為臨界擱淺情節，本文使用數學模型分析此船擱淺過程，得到臨界前進初速度。擱淺可分成兩階段，第一階段為船舶動量改變，第二階段為船舶於海床上滑動。在此兩階段中，船舶動能散失於摩擦海床、船艙結構塑性壓潰，以及艏部抬昇造成俯仰差加大。隨後本文進行數個耗時的非線性有限元素分析，進一步修正此數學模型。此修正遇之數學模型可以快速分析船舶擱淺問題，最後可得到臨界擱淺情節以及臨界前進初速度。船體樑強度亦在臨界情節下加以檢視，結果顯示即使艏部抬昇、局部損傷造成泛水，船體樑強度仍然足夠。