A method for progressive structural crashworthiness analysis under collisions and grounding
Introduction
Accidental limit states (ALS) potentially lead to a threat of serious injury or loss of life, pollution, damage and loss of property or significant financial expenditure. The intention of ALS design is to ensure that the structure is able to tolerate specified accidental events and, when accidents occur, it subsequently remains structural integrity for a sufficient period under specified (usually reduced) environmental conditions to enable evacuation of personnel from the structure, control of undesirable movement or motion of the structure, temporary repairs, safe refuge and firefighting in the case of fire and explosion, and minimizing outflow of cargo or other hazardous material to take risk mitigation and recovery measures to take place as relevant [1], [2].
Limit state design and safety assessment associated with collisions and grounding is typically based on the energy absorption capability of the structure until the accidental limit state is reached. Since the energy absorption capability can be obtained by integrating the area below the reaction forces versus penetration curve of the structure, the progressive structural crashworthiness analysis involving crushing, yielding, and fracture must be carried out to obtain the resulting force-penetration curve of the structure in the accidental event.
Further, the risk assessment associated with ALS needs to identify the consequence of accidental events, because the reaction forces versus penetration relationships of a structure under collisions and grounding are used as a basis of the consequence analysis.
While the finite element method is a powerful tool for the simulations of structural crashworthiness due to collisions and grounding [2], [3], [4], [5], [6], it may require a lot of modeling and computational efforts.
The aim of the present paper is to introduce an efficient and accurate numerical method for structural crashworthiness analysis of ships and ship-shaped offshore structures under collisions or grounding (stranding), which involves crushing, yielding, and fracture. The analysis method presented has been implemented into ALPS/SCOL [7] program, being linked with MAESTRO [8] for pre- and post-processing of the related computations.
Application examples of the method are presented by a comparison with experimental results on ship-shaped test structures under crushing loads or collisions or stranding actions.
Section snippets
Theory for structural crashworthiness analysis
ALPS/SCOL [7] is a computer program for the progressive structural crashworthiness analysis under collisions and grounding. It applies the idealized structural unit method (ISUM) [1], [2]. The following three types of ISUM elements are employed for ALPS/SCOL analysis, namely.
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Rectangular plate element;
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Beam-column element;
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Gap/contact element.
It is noted that the theoretical formulation for the old version of the three types of ISUM elements above is presented in Paik and Pedersen [9], and Paik
Structural crashworthiness analysis for square tubes under crushing loads
Paik et al. [11] conducted a series of crushing tests on ship-shaped structure models such as unstiffened plate structures, longitudinally stiffened plate structures, transversely stiffened plate structures, and orthogonally stiffened plate structures, under crushing loads, until and after crushing takes place. Crushing loads were applied uniformly to the cross section of each tube.
Fig. 4 shows the four types of square tubes used for the tests. The aim of their tests was to investigate the
Structural crashworthiness analysis for a double-skin plated structure under collisions or stranding
Paik et al. [15] carried out an experimental study on a double-skin-plated structure quasi-statically penetrated by a circular cone type indentor, with varying the plate thickness and the collision location. Fig. 9 shows a schematic view of the test structure and the photograph of the actual test setup. The test structure is composed of plate elements only. The test results can also be applied to the study of stranding which is a specific type of grounding.
The details of the test are presented
Concluding remarks
For accidental limit state design and strength assessment of thin-walled structures under collisions and grounding, the progressive crashworthiness analysis involving crushing, yielding, and fracture must be carried out. This kind of the analysis is also required for the risk assessment associated with such accidental events, because the consequence analysis during the risk assessment is typically based on the results of the progressive crashworthiness analysis.
In the present paper, an
Acknowledgments
The present study was undertaken at the Ship and Offshore Structural Mechanics Laboratory (http://alps.ac), Pusan National University, Korea, which is a National Research Laboratory funded by the Korea Ministry of Science and Technology (No. M10600000239–06J00000–23910). The authors are pleased to acknowledge the support of Pusan National University. The present paper was presented at International Conference on Advancements in Marine Structures, 12–14 March 2007, Glasgow, UK.
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