The loading specification for this problem includes descriptions of the explosive charge, the fluid medium in which the wave propagates to the structure, and the geometry of the charge with respect to the structure.
In Abaqus the time histories of pressure, its derivatives, and the motion of the explosive gas bubble are defined using the Geers-Hunter model. This model is invoked using the bubble-type amplitude. Under this option material properties of the explosive, its mass, its distance from the free surface, and some other control parameters are specified. The data on this option are used to govern a separate bubble dynamics time integration operation, performed as part of the preprocessing. Parameters defined on this option do not affect the rest of the analysis. Here a charge of 100 kg is used, with model parameters set to suppress wave loss effects within the bubble simulation. An initial depth of 65 m is specified: this affects the oscillation of the gas bubble and the duration of the bubble dynamics, since the solution naturally terminates when the bubble reaches the free surface. In this analysis, however, the bubble simulation time is cut off at 0.6 seconds. The bubble migration is defined to be along the z-axis. Default values for the bubble dynamics time integration parameters are used.
The actual loads on the structure are defined using the incident wave and the associated incident wave reflection. The incident wave defines the distributed time-varying loads within an analysis step on the structural surface, due to the specified parameters. Only the surface defined for the beam elements and the reference load magnitude need to be indicated, as is the case for most distributed loads in Abaqus. The incident wave reflection defines any planes outside the computational domain for the purpose of calculating additional incident wave loads due to reflections. Here a “soft” (zero total pressure) reflecting plane is defined, located 65 m from the original position of the source and oriented normal to the z-axis. The original position of the source point is defined as (50, 15, −15), and the standoff point is defined as (50, 3.536, −3.536). The fluid properties, used for propagation of the wave across the structure, are given as mass density = 1025 kg/m3 and bulk modulus = 2.30635 GPa.