This paper is a sequel to the previous two papers by the authors presented at SNAME annual meetings in 2012 and 2013. The key tasks for measuring and managing risks associated with hydrocarbon explosions include defining explosion loads and computing structural responses. In industry practice, such response analysis often involves applying uniformly distributed explosion loads to structures according to their nominal design values. However, uniformly distributed loads based on nominal values of structural design may not always fully reflect the actual situations of real explosion accidents, mainly because the actual characteristics of both explosion loads and structural responses are extremely nonlinear. Therefore, it is highly desirable to identify the non-uniform distributions of explosion loads and directly apply them to structures for the response analysis. To accomplish this, technical challenges must be met in terms of refined computations for loads, structural responses and interfaces between load definitions and structural analyses. This study develops a new procedure to resolve such challenges. In this procedure, FLACS computational fluid dynamics (CFD) simulations are applied to the characterization of blast loads. ANSYS/LS-DYNA nonlinear finite element methods (using plate-shell elements) are applied for nonlinear structural response analysis, and a computer program named FLACS2DYNA is developed to automatize the direct export of the FLACS simulations to the ANSYS/LS-DYNA computations. The contribution of this study is demonstrated through an applied example using a hypothetical topside structure of a VLCC-class FPSO that is exposed to hydrocarbon explosions. This example shows that the developed procedure can enable fast, accurate and reliable nonlinear structural response analysis, and subsequently allow better assessment and management of explosion risks.
Methods for Nonlinear Structural Response Analysis of Offshore Structures with Passive Fire Protection under Fires
