波浪負荷下之遊艇結構強度分析

Abstract

於遊艇結構設計時，需選擇適當、合理的設計外力，才能得到正確的遊艇結構；本文依遊艇於不同航速下，將其所受的外力分成兩種：(1)低航速時的排水型波浪負荷 (2)高航速時的滑航型波浪負荷；並選擇適當的流體動力軟體取得此兩種外力，本文使用DNV公司發展的WASIM取得排水型波浪負荷，及使用台灣大學工程科學暨海洋工程學研究所船舶運動實驗室自行撰寫的非線性截片理論程式取得滑航型波浪負荷，並將所得外力施加於目標遊艇有限元素模型上，進行動態結構分析。除此之外，本文亦計算目標遊艇於ISO 12215-5法規和DNV HSLC法規的設計壓力，與程式所得壓力做比較，並將其施加於目標遊艇有限元素模型上，進行靜態結構分析。所得結構分析結果，所有應變皆小於容許應變，顯示目標遊艇尚有輕量化的空間。 而於目標遊艇有限元素模型中，以等效樑的設定方式取代實際樑的形狀、尺寸；但是，樑的強度並非只有樑本身所提供，樑下之板亦提供了一定程度的強度，故等效樑需考慮樑下板的寬度於其設定條件中；而如何決定等效板的寬度，本文以目標遊艇中的25根樑做探討，歸納出一公式，希望未來能供大家參考。

When designing the structure of a yacht, we have to select the appropriate and reasonable design external loads to evaluate the structure of a yacht. Consequently, based on the speed of the target yacht when sailing, the researcher divides the external loads, a yacht may be suffered, into two types: (1) displacement wave pressure under low speed (2) planing wave pressure under high speed; afterwards, two appropriate software would be used to obtain these two external loads. In this paper, WASIM, which is developed by DNV Company, is used to obtain the displacement wave pressure, while nonlinear strip theory program, established by the ship motion lab in NTU ESOE, is employed to get the planing wave pressure. Two types of pressure mentioned are then applied to a finite element model of the target yacht to perform the dynamic structure analysis. Besides, the design pressure of the target yacht is also calculated according to ISO 12215-5 and DNV HSLC code. The results would be compared to the software ones and then be imposed to the finite element model to perform static structure analysis. The results of structure analysis demonstrate that all of the strains of the target yacht are all less than the allowable strain, which indicates the practicability of further weight deduction. Regarding the finite element model of the target yacht, a generalized beam model is used to replace the actual establishment of the beam shape; however, when it comes to the beam strength evaluation, the beam is not the only element to be concerned, since the plate below plays a comparably important role as well, the width of the plate should be considered in generalized beam settings. As for the equivalent width of the plate, a formula is induced based on the survey of the 25 sample beams of the target yacht, in hope of providing future references to other researchers.