FINITE-ELEMENT ANALYSIS OF THE QUARTER SCALE ADVANCED DOUBLE-HULL DESIGN

The design of advanced unidirectionally stiffened double hull surface ships is motivated by economic, military civilian and environmental co ncerns, Major concerns include economical producibility, reduced signa ture, enhanced survivability and damage resistance to grounding. Verif ication of structural analysis capabilities, identification of collaps e mechanisms and evaluation of structural integrity are issues that ne ed to be addressed. Congress established the Advanced Double Hull Tech nology Project following the Oil Pollution Act of 1990, and provided F Y 92 and FY 93 funding to investigate double hull technology for naval surface ships and commercial application of ecologically sound bulk f uel carriers. As part of this project the Office of Naval Research (ON R) tasked the Carderock Division of the Naval Surface Warfare Center ( CD/MSWC) to evaluate the crash-worthiness of the double hull concept i n stranding incidents. This work included a series of quarter-scale st randing experiments conducted at the National institute of Standards a nd Technology (NIST). Finite element analysis was performed to demonst rate the accuracy of non-linear, large deflection numerical modeling b y comparison with the experimental results. The Advanced Double Hull ( ADH) design features longitudinal web stiffeners with an inner-outer h ull spacing of 79 inches. In this investigation, a quarter scale model of a representative section of the hull with an inner-outer hull spac ing of 18.5 inches was used to analyze stranding. The structural perfo rmance and load transfer mechanisms of the ADH quarter scale model dur ing a simulated stranding event were the primary objectives of the ana lysis. In the stranding event, an object on the bottom of a harbor or shallow waterway was simulated by a spherically tipped conical penetra tor. The penetrator initially contacted the outer hull, A 30 inch disp lacement of the penetrator was applied beyond the initial point of con tact. Explicit finite element methods were utilized to determine the s tructural response and collapse mechanisms produced by the stranding e vent, Large strain elastic-plastic constitutive response and geometric non-linearity were accounted for in the finite element analysis. The progressive penetration leads to outer hull rupture, longitudinal web deformation, contact between the outer hull and the webs, contact betw een the outer and inner hull and deformation of the inner hull. The in ner hull deformed 11.5 inches inward during the finite element analysi s and was deflected without fracture to a predicted maximum load of 1, 060,040 Ibs. The levels of deformation, fracture and plastic energy di ssipation of the analysis model compared favorably with the experiment al results. Detailed examination of the finite element results provide d an understanding of the structural elastic-plastic performance assoc iated with stranding and a validated methodology for further use by de signers and analysts.