Using slides from Shahbaz Memon, Dorothée Vallot and Thomas Zwinger HPC use case: Glaciology/Ice sheet modelling and supporting scientific workflows Helmut Neukirchen helmut@hi.is University of Iceland Using slides from Shahbaz Memon, Dorothée Vallot and Thomas Zwinger

Helmut Neukirchen: Ice sheet modelling / Scientific workflows About me Helmut Neukirchen. Professor of Computer Science and Software Engineering, University of Iceland. Software Engineering for Distributed Systems, e.g. HPC/eScience such as scientific workflows. Collaboration with Jülich Supercomputing Centre, Germany. Morris Riedel coming every year as guest professor to Uni Iceland. Worthwhile as associated partner of NeIC just like partners in Estonia. Organised HPC Workshop in Iceland this August. Supported by NeIC, success according to participant evaluation. Helmut Neukirchen: Ice sheet modelling / Scientific workflows

Helmut Neukirchen: Ice sheet modelling / Scientific workflows Context of use case NordForsk funded Nordic Centre of Excellence eSTICC (eScience Tools for Investigating Climate Change at High Northern Latitudes). Climate modelling (millions of CPU hours needed in Norway), Ice sheet modelling (to predict sea level rise): 2 senior researchers: Helmut Neukirchen (Scientific workflows, Uni Iceland), Thomas Zwinger (Glaciology, CSC, Finland). 2 PhD students: Shahbaz Memon (Scientific workflows, Uni Iceland and Jülich Supercomputing Centre, Germany), Dorothée Vallot (Glaciology, Uni Uppsala, Sweden). Helmut Neukirchen: Ice sheet modelling / Scientific workflows

Use case: Glacier flow and calving Ice deformation and sliding Modelled as a continuous process (finite element method). Calving Modelled as discrete process (discrete element model). Helmut Neukirchen: Ice sheet modelling / Scientific workflows

Helmut Neukirchen: Ice sheet modelling / Scientific workflows Elmer/Ice Elmer: Finite Element Method (FEM) Software. Elmer/Ice add-on for modelling ice sheet flow. Mainly developed by Thomas Zwinger at CSC, Open source, Parallel processing. In FEM, finite elements may have different sizes (and even shapes). Adaptive mesh of finite elements: fine grained where a lot of stress occurs, coarse where minor stress. Helps to save CPU time. 5 Helmut Neukirchen: Ice sheet modelling / Scientific workflows 5

Helsinki Discrete Element Model (HiDEM) for ice calving Particle-based model of calving [Jan Åström et al.: A Particle-based simulation model for glacier dynamics, Cryosphere, 2013]. Parallel processing, Closed-source. Only available on CSC cluster Sisu. All particles of same size. High spatial (in the size of the cracks) and temporal (spatial scales divided by speed of sound) resolution. Computationally very expensive. Glacier divided into discrete particles as an initially dense package with random properties to simulate cracks and flaws in ice Elastic fracture strain 𝜀_𝑏 Change of stability between sub- to super-critical states Iterations over time (time step < 10-4 s) Water depth Ice Water 6 Helmut Neukirchen: Ice sheet modelling / Scientific workflows 6

Scientific workflow: coupling FEM & DEM Shared Preprocessing Serial Generate Mesh Serial ElmerSolver Parallel Cluster 1 Elmer-> Particle Serial Loop Until Num. Observations Originally: 2000 Lines of code shell script Parallel Particle Calving Cluster 2 Particle-> Elmer Serial Workflow engine of UNICORE middleware Helmut Neukirchen: Ice sheet modelling / Scientific workflows

Use Case: Kronebreen glacier, Spitsbergen, Svalbard One of the largest glacier streams on Svalbard. Draining about 690 km2. Average speed: 2 m/d. Status: Executed models coupled via shell script by Dorothée Vallot. Many iteration desirable: comparing model with reality observed for every 11 days for 3 years. 5000 CPU h FEM + 20 000 CPU h DEM for every iteration. Abstract scientific workflows developed without any allocated CPU time by Shahbaz Memon. Tested using local runs with dummy calving. Kronebreen is a glacier located at the western side of Spitsbergen, Svalbard. It is one of the largest glacier streams on Svalbard, draining about 690 square kilometers. The glacier moves with an average speed of two meters per day. Helmut Neukirchen: Ice sheet modelling / Scientific workflows 8

Helmut Neukirchen: Ice sheet modelling / Scientific workflows Status and Conclusion UNICORE middleware for workflows operational at CSC since last week. Elmer/Ice and HiDEM anyway installed at CSC. Now, waiting for CPU cycle allocation at CSC. 200 000 h applied for via Dellingr last Thursday. Would allow a few iterations of coupled ice sheet models for Kronebreen. Both needed by Dorothée Vallot to finish her PhD on modelling Kronebreen and by Shahbaz Memon to evaluate his workflow abstraction. Outlook: generic one-click ice sheet simulation possible for glaciologists via Shahbaz’s workflow. May result in need of even further CPU hours. Note: in addition to glaciologists in Uppsala and Helsinki, also glaciologists at University of Iceland do extensive simulations (coupled climate/ice sheet). Use cluster from Danish Met. Office (located at Icelandic Met. Office), but also Icelandic HPC cluster Garpur for smaller trial runs. Helmut Neukirchen: Ice sheet modelling / Scientific workflows