FEA Boundary Buffer for Underwater Explosion Simulation
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Solution Overview
Problem
Current methods for numerically simulating underwater explosions using Arbitrary Lagrangian-Eulerian based finite element analysis (FEA) face issues with stress wave reflections at the model boundary, leading to incorrect results, which are not fully mitigated by existing approaches that either enlarge the model or apply artificial stresses.
Innovation Solution
A modified FEA model is created with an extra layer of border nodes and elements outside the original boundary, where simulated fluid behaviors are computed and stored in lookup tables, allowing interpolation of new border elements' behaviors based on master elements, thereby avoiding stress wave reflections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of stationary object
If the FEA model boundary is placed close to the blast source to reduce model size, then computing resources are saved, but stress wave reflections at the boundary cause incorrect simulation results
Solution Approach 1:
The fluid domain is segmented into two distinct regions: an inner region containing the original FEA model with the blast source, and an outer region consisting of buffer elements that absorb stress waves. This segmentation allows the model to maintain a compact size while preventing harmful reflections through the buffer zone.
Solution Approach 2:
Buffer elements are introduced as an intermediary layer between the blast source and the model boundary. These buffer elements act as a mediator that absorbs and dissipates stress waves, preventing them from reflecting back into the computational domain and corrupting the simulation results.
2Reliability
If the FEA model is enlarged to move the boundary away from the blast source, then stress wave reflections are reduced, but computing resources increase
Solution Approach 1:
The buffer elements are applied locally only at the boundary regions where stress wave reflections occur, rather than enlarging the entire model. This localized approach maintains high simulation accuracy while minimizing the increase in computational resources required.
3Reliability
If artificial normal and shear stresses are applied at the FEA model boundary to compensate for stress wave reflections, then some reflection effects are reduced, but the method requires many ad hoc techniques that are not easy to practice
Solution Approach 1:
The buffer elements are designed to automatically absorb stress waves through their inherent material properties and geometric configuration, without requiring complex artificial stress applications or ad hoc correction techniques. The buffer zone self-regulates the stress wave behavior, simplifying the overall simulation methodology.
Data Source
AI summary
Characteristics of a blast source and a FEA model representing a surrounding fluid domain are defined. One layer of new border nodes and elements are created outside of the fluid domain's original outer boundary formed by the original border elements. Each new border element/node is associated with one of the original border elements/nodes as corresponding master element/node. At each time step of a time-marching simulation of an underwater explosion, simulated fluid behaviors are computed for all but the new border elements. The computed fluid behaviors of each original border element are saved into a corresponding lookup table configured to store the computed fluid behaviors for a predefined number of time steps in a first-in-first-out manner. Simulated fluid behaviors of each new border element are determined by interpolating, with the calculated blast wave propagation time from the master element, the stored fluid behaviors in the corresponding master element's lookup table.