S-ALE, full name Structured Arbitrary Lagrangian-Eulerian, is essentially a numerical method that introduces structured mesh + multi-material filling + improved advection algorithms within the ALE framework.
While maintaining the same theoretical foundation as traditional ALE (advection, remapping, interface reconstruction, FSI coupling), S-ALE achieves faster computation speed, lower memory consumption, and more stable simulation performance through automated mesh generation and more efficient search/sorting algorithms.
I. Differences Between S-ALE and Traditional ALE Algorithms
Traditional ALE requires users to generate the complete mesh in a pre-processor, then export node and element lists to the input file. For large-scale models, this results in huge input file sizes, long read-in times, and inconvenient mesh modifications.
S-ALE is specifically optimized for structured meshes (all elements are regular hexahedra with mutually perpendicular faces and non-uniform spacing allowed). The main advantages include:
1. Automated Mesh Generation: No need to manually list all nodes and elements. Only a few control points are needed to define the mesh geometry, and the solver automatically generates it during the read-in phase.
2. Higher Computational Efficiency: Faster search and sorting algorithms mean the same model typically runs faster with significantly reduced memory usage.
3. Cleaner Input Files: Large-scale ALE problem input deck volumes are greatly reduced, and modifying mesh geometry is more convenient.
4. Better Stability: Specialized implementation for structured meshes reduces certain numerical instability issues.
5. High Usability: Users familiar with traditional ALE can get started quickly. Most ALE keywords remain compatible, with only a few new specialized cards added.
S-ALE supports SMP, MPP, and hybrid parallelism, suitable for typical scenarios such as explosions, ballistic penetration, sloshing, and fluid-structure coupling. However, it requires the mesh to be a regular box-shaped structure, i.e., rectangular prism shape, and is not suitable for highly complex unstructured geometries. For complex geometries, traditional ALE or ICFD are still recommended.
II. S-ALE Mesh Generation
Mesh generation mainly relies on two keywords:
1. *ALE_STRUCTURED_MESH_CONTROL_POINTS: Used to define mesh spacing control points along the three directions of the local coordinate system.
2. *ALE_STRUCTURED_MESH: Invokes mesh generation and activates the S-ALE solver.
Usage example: Assuming we need to define a 200×100×50 S-ALE mesh region with mesh size of 1.
The POINTS keyword definition example is as follows (actually defining three lines, where the length of each line is determined by the coordinates of the start and end points):
As shown in the figure above, the two points are (0, 0) and (200, 0), numbered from 1 to 201, meaning the length of 200 is divided into 200 parts, with element size of 1.
The definitions for the other two directions are as follows:
The definition of *ALE_STRUCTURED_MESH is as follows, mainly defining mesh ID and the three control points. Click Draw to display the defined ALE mesh:
III. Multi-Material Group Definition
Old: *ALE_MULTI-MATERIAL_GROUP: Traditional ALE multi-material group definition, compatible with S-ALE
New: *ALE_STRUCTURED_MULTI-MATERIAL_GROUP: S-ALE multi-material group definition
IV. Fluid-Structure Coupling Algorithm Definition
Old: *CONSTRAINED_LAGRANGE_IN_SOLID: Traditional fluid-structure coupling definition, compatible with S-ALE
New: *ALE_STRUCTURED_FSI: S-ALE dedicated fluid-structure coupling keyword.
Compared to the traditional fluid-structure coupling keyword, FSI requires fewer parameters, and this keyword only uses penalty function formula coupling, similar to the combination of CTYPE=4 and 5 in *CONSTRAINED_LAGRANGE_IN_SOLID. In S-ALE, *ALE_STRUCTURED_FSI is officially recommended, as the new keyword provides better leakage control.
V. Volume Filling
Old: *INITIAL_VOLUME_FRACTION_GEOMETRY
New: *ALE_STRUCTURED_MESH_VOLUME_FILLING
After comparison, the difference between the two has minimal impact on calculation results.
Of course, in addition to the main keywords mentioned above, there are some auxiliary settings, such as mesh refinement, cutting, and other operations, but the implemented operational functions are limited. You can open LSPP’s Model to view all keywords related to the S-ALE method, as shown below.
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