When to Use SALE: Practical LS-DYNA Insights for FSI Problems
Fluid‑structure interaction (FSI) problems often sit at the most challenging end of simulation. Fast‑moving fluids, deforming structures, and highly transient events push both modelling approaches and solver performance to their limits.
In this blog, EDRMedeso specialists address common and practical questions about SALE (Structured Arbitrary Lagrangian‑Eulerian) methods in LS‑DYNA, focusing on when SALE is the right choice, how it compares to other FSI approaches, and what engineers should pay attention to when validating results.
Why engineers turn to SALE in the first place
SALE methods combine aspects of both Lagrangian and Eulerian formulations, making them well suited to problems where large fluid motion interacts with structures over short time scales.
Unlike fully implicit FSI approaches, SALE uses explicit time integration, which makes it particularly effective for:
- High‑energy events
- Rapid transients
- Short‑duration phenomena
This is why SALE is often considered for impact‑like or highly dynamic fluid‑structure problems where traditional approaches may struggle with stability or computational cost.
Validation still matters – even with advanced methods
One of the key messages is clear: advanced methods do not remove the need for careful validation.
The same principles used in other simulations still apply:
- Energy conservation should be checked
- Reaction forces should be monitored
- Overall physical behaviour should make sense
For FSI problems, the experts also highlighted the importance of leakage checks. If material is allowed to flow out of the domain and no ALE boundary conditions are applied, apparent energy loss can occur. Leakage‑related quantities can be evaluated using DATABASE_FSI outputs, such as gx, gy, and gz.
Where measurement data is available, comparing simulation results with experimental data remains one of the most effective validation approaches.
Can SALE be used for rotating objects in water?
This is a common and very practical question.
SALE can be applied to rotating objects in water that are subsequently stopped, including cases where added mass, damping, and structural stresses are of interest. However, it’s important to note that the initialisation is critical.
Engineers are advised to:
- Establish a steady‑state flow solution first
- Then perform the stopping or transient event simulation
Even with correct setup, these simulations can become computationally expensive. In some cases, ICFD may be a more efficient alternative, depending on the problem goals.
SALE vs traditional FSI: not a competition
Another important clarification is that SALE is not a replacement for all FSI methods.
In practice, SALE should be viewed as complementary to:
- FSI with LS‑DYNA Implicit and ICFD
- Coupled approaches using Ansys Mechanical and Ansys Fluent
SALE excels in scenarios where explicit time integration and short‑term dynamics dominate. For longer‑duration or quasi‑static problems, other methods may be more appropriate. Choosing the right approach is ultimately about efficiency, robustness, and the specific physics being studied.
Tool availability and practical adoption
The current status of tool availability within the Ansys ecosystem is that SALE capabilities have been introduced gradually in Ansys Mechanical, with early exposure in 24R2 and more complete mesh workflows implemented in 2025R2. Further improvements are expected in subsequent releases.
For engineers, this means SALE workflows are becoming increasingly accessible, but understanding when and how to use them remains essential!
The key takeaway
SALE methods in LS‑DYNA are powerful tools for solving demanding fluid‑structure interaction problems, especially those involving fast, high‑energy events. Their real value emerges when engineers understand both their strengths and their limitations.
Used in the right context, SALE provides insight that would otherwise be difficult (maybe impossible) to obtain. Used without careful validation or problem selection, it can add unnecessary complexity. As with all advanced simulation techniques, success lies in choosing the right tool for the right problem.
Watch our on-demand webinar ‘Setting Up Sale Models in Ansys Mechanical’
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