Some Experiences on Parallel Finite Element Computations Using IBM/SP2 Yuan-Sen Yang and Shang-Hsien Hsieh National Taiwan University Taipei, Taiwan, R.O.C.

Contents Parallel Substructure Method Three Issues : –Mesh Partitioning –Nodal Renumbering within Substructures –Solution of Interface DOFs Conclusions

Parallel Substructure Method Partition a structure into several substructures. Assign each substructure to a processor. Matrix assembly & static condensation within each substructure.

Parallel Substructure Method (cont.) Solve the displacements of interface DOFs. Solve the displacements of internal DOFs in each substructure. Perform force recovering in each substructure.

Mesh Partitioning Requirements –Automatic Partitioning –Handling regular & irregular meshes. –Balanced distribution of number of elements. –Minimization of number of interface nodes.

Experiences (Mesh Partitioning) GR, RST, METIS are used in this work. Balanced distribution of number of elements is achieved. Condensational load are unbalanced. RST

Substructural Nodal Renumbering Purpose: –To reduce the skyline of substructure matrix. Constraint: –Interface nodes must be numbered after internal nodes Reversed Cuthill-Mckee (RCM, Liu & Sherman 1975) is modified and used.

Experiences (Substructure Nodal Renumbering) Help to Reduce the condensational loads. Rarely balance the condensational loads among processors. Without Substructure Nodal Renumbering With modified RCM Substructure Nodal Renumbering 30STORY. RST. With 4 processors RST

Solution of Interface DOFs Achieving high parallel efficiency for linear equation solver is not an easy task. When N P increases N I increases Parallel Efficiency decreases

Experiences (Solution of Interface DOFs) In this work, a sequential direct method( Cholesky decomposition) is used. N I is affected by both N P and the performance of the partitioning algorithm.

Conclusions Mesh partitioning –Computational loads of each processor is not necessarily proportional to its number of elements. –Minimization of interface nodes reduces the interface equations and usually improves the parallel efficiency. Substructural nodal renumbering –Substructural nodal renumbering always reduces the condensational loads. –But rarely balance the condensational loads among procesors. Parallel solution of interface DOFs –High-efficiency parallel solvers of interface equations are needed for improving the efficiency of parallel substructure method.

Acknowledgement This research is supported by the National Science Council of R.O.C., under the project Nos. NSC E and NSC E The parallel computations are performed on IBM/SP2 comupters of National Center for High-performance Computing, Hsin-Chu, Taiwan, R.O.C.

IBM/SP2 in NCHC Model –IBM POWER2 SuperChip (P2SC) Floating Peak Performance –480-MFLOPS Memory –128 Mbtyes per node