Subject: Review for C505 From: Manish Parashar Date: Sat, 23 Jun 2001 15:05:30 -0400 To: Geoffrey Fox CC: Manish Parashar Dear Geoffrey, Here is my review. Sorry for the delay. Best regards Manish =========================================================================== Manish Parashar Office: 504 CoRE Dept. of Electrical & Computer Engr. Phone: (732) 445-5388 Rutgers University Fax: (732) 445-0593 94 Brett Road Email: parashar@caip.rutgers.edu Piscataway, NJ 08854-8058 http://www.caip.rutgers.edu/~parashar =========================================================================== C505: Thermal Convection Analysis in a Rotating Shell by a Parallel FEM - Development of a Thermal-Hydraulic Subsystem of GeoFEM Hiroaki Matsui and Hiroshi Okuda Department of Research for Computational Earth Science, Research Organization for Information Science & Technology (RIST), Tokyo Department of Quantum Engineering and System Science, The University of Tokyo, Tokyo, Japan Email: matsui@tokyo.rist.or.jp Overall recommendation: reject Review: This paper presents a numerical simulation of thermally driven convection in a rotating spherical shell modeled on the Earth ’s outer core using the Thermal-Hydraulic subsystem of GeoFEM. These simulations have been typically done using spherical harmonic expansions. The authors motivation is using FEM is to make it suitable for massively parallel computations. In this paper, the authors concentrate on comparing the results generated by the parallel FEM simulations to those produced by the spectral harmonics expansion. In the results, the authors demonstrate that the results differ by about 10% that the authors attribute to differences in the spatial resolution, radial resolution, and initial temperatures in the two simulations. Furthermore, the authors mention that the radial resolution in the FEM formulation can cause “serious problems” and require a smaller time step in this case – making it computationally more expensive. While the paper is interesting and appears technically sound, I have some concerns about the contributions and suitability of the paper given the focus of the journal and those of the special issues (as listed at http://www.quakes.uq.edu.au/ACES/WG/WG5/index.html) The paper does not address the parallel formulation of the problem, its parallel FEM implementation or the issues/requirements/challenges that arise when moving this class of problems to massively parallel platforms. It is only mentioned that the implementation uses the GeoFEM package and relies on this package to support parallelism. The parallel runtimes listed are for 32 processors (not “massively parallel”) and show a scalability of about 2.7 when moving from 8 to 32 processor. Furthermore, the results indicate that the FEM simulation is at least an order of magnitude more expensive than the spectral method simulation. This is attributed to the smaller time step that is required for the FEM case, and also to the inefficiency of the parallel FEM code (attaining only 5% of peak). The authors do mention that the FEM formulation is new. The overall paper requires some effort to read and understand and has many grammatical and spelling errors. A few of these are listed below. I would suggest that a paper that focuses on the requirements/challenges for a parallel formulation of the problem and possibly an investigation of the overheads and lack of scalability of the current GeoFEM based implementation would be more appropriate for this journal. Presentation Changes: The paper has many grammatical errors that make it quite difficult to read. A few typos are listed below 1. Page 1, section 1, line6 – should be “ Furthermore, the dynamo process is not only a complicated nonlinear system…” 2. Page 1, section 1, last line – should be “Most of these simulations, however, have applied the….” 3. Page 2, section 1, line 4 – should be “…. the finite difference method is applied, however they have considered…” 4. Page 2, section 1, line 12 – should be “…. rotating spherical shell on massively parallel computers.” 5. Page 2, section 1, line 21 – should be “… convection column which are parallel….” 6. Page 2, section 1, line 22 – should be “… the columns propagate westward in both cases…” 7. Page 2, section 2, line 4 – should be “…. and rotates with a uniform angular….” 8. Page 5, section 2, line 9 – should be “… each triangle is divided into three…” 9. Page 6, section 2, line 11 – should be “… a large truncation error…” 10. Page 6, section 3, line 12 – should be “… which are parallel …” 11. Page 7, section 3, line 3 – should be “… Z-component…” 12. Page 7, section 3, line 6 – should be “… position of each convection column…” 13. Page 9, section 3, line 12 – should be “… is estimated by the phase…” 14. Page 9, section 3, line 15 – should be “… the convection pattern propagates rapidly in the case of GeoFEM…” 15. Page 10, section 4, line 2 – Table number missing. 16. Page 10, section 4, line 3 – should be “…a 10 % difference is seen in several values in the results…” 17. Page 10, section 4, line 5 – remove “In these differences,” 18. Page 10, section 4, line 6 – should be “… around both the boundaries…” 19. Page 12, units for column 3 missing in table 2.