Concrete-filled double-skin steel tubular (CFDST) structures are a type of composite structure that consists of two concentric steel tubes (an inner and outer steel tube) with concrete filled in the annular space between them. These structures are increasingly used in offshore, marine, and defense-related applications due to their excellent strength-to-weight ratio, enhanced energy absorption capacity, and corrosion resistance.

When subjected to underwater explosions (UNDEX), which are characterized by high-intensity shock waves and dynamic loading, CFDST structures experience complex stress distributions and potential failure modes. Understanding their behavior under such extreme conditions is critical for designing resilient infrastructure in naval and offshore engineering, including submarines, offshore platforms, and underwater pipelines.

Purpose of the Numerical Investigation:

The numerical investigation typically uses finite element methods (FEM) and simulation tools such as ABAQUS, LS-DYNA, or ANSYS AUTODYN to model and predict the structural response of CFDST systems when exposed to underwater blast loading. In this example, the ABAQUS software is selected.

The primary objectives include:

1. Assessing blast resistance: How well the CFDST structure can withstand the shock wave pressure and impulse from an underwater explosion.

2. Understanding failure mechanisms: Identifying the nature and location of failure, whether it’s local buckling, spalling, delamination, or global structural collapse.

Significance:

This investigation provides essential insights into the blast-resistance performance of advanced composite structures in marine and defense environments. The findings help improve:

• Structural safety and survivability under extreme events.

• Design codes and blast-resistant design practices.

• Material and construction efficiency by reducing over-conservatism in design.

In this example, the Coupled Eulerian-Lagrangian (CEL) model is considered to model water, air, and explosive material.

This example is close to the paper here: Numerical simulation of concrete-filled double skin steel tubular (CFDST) structure subjected to underwater explosion loading in Abaqus