Parametric And Optimization Study: OpenFOAM And Dakota - Cineca

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Workshop "HPC enabling of OpenFOAM for CFD applications"CINECA, Casalecchio di Reno, Bologna, 26 November 2012Parametric and Optimization study:OpenFOAM and DakotaIvan Spisso,, CFD Numerical AnalystSuperComputing Applications and Innovation (SCAI) DepartmentCINECA

Outline of the presentation DAKOTA in a nutshell (1) The loosely coupled loop of DAKOTA (1) Key DAKOTA Capabilities (4) Parallelism in Dakota (6) DAKOTA on PLX: job submission, input file and loosely coupled loop (3) Advanced Simulation Code Interfaces: OpenFOAM (2) Simulation Control and quality check (2)

Dakota in a NutshellDesign and Analysis toolKit for Optimization and Terascale Applicationsincludes a wide array of algorithm capabilities to support engineeringtransformation through advanced modeling and simulation.Adds to simulation-based answering fundamental science and engineeringquestions: What are the crucial factors/parameters and how do they affectmetrics? (sensitivity) How safe, reliable, robust, or variable is my system?(quantification of margins and uncertainty: QMU, UQ) What is the best performing design or control? (optimization) What models and parameters best match experimental data?(calibration) All rely on iterative analysis with a computational model for thephenomenon of interest

Automated Iterative AnalysisAutomate typical “parameter variation” studies with ageneric interface to simulations and advanced methodsDAKOTAOptimization, sensitivity analysisparameter estimation, uncertain quantificationParameters(design, state)The loosely-coupled loopResponsemetricsComputational Model (simulation)Black box: any code: mechanics, circuits,high energy physics, biology, chemistry Semi-intrusive: Matlab, Python, multi-physics,OpenFOAM Can support experimental testing: examine many accidentconditions with computer models, then physically test a fewworst-case conditions.

Key DAKOTA Capabilities Generic interface to simulations Time-tested and advanced algorithms to address nonsmooth,discontinuous, multimodal, expensive, mixed variable, failure-prone Strategies to combine methods for advanced studies or improveefficiency with surrogates (meta-models) Mixed deterministic / probabilistic analysis Supports scalable parallel computations on clusters !! Object-oriented code; modern software quality practices JAGUAR 2.0, new graphical user interface in Java, based on EclipseIDE/Workbench. Windows, Mac, Linux support. Additional details: Software downloads: stable releases and nightly builds (freely availableworldwide via GNU LGPL) Installed on PLX (module load profile/advanced autoload dakota) likeSandia National Lab

Optimization GOAL: Vary parameters to extremize objectives, while satisfyingconstraints to find (or tune) the best design, estimate best parameters,analyze worst-case surety, e.g., determine:– delivery network that maximizes profit while minimizing environmentalimpact– case geometry that minimizes drag and weight, or maximize thepressure force, yet is sufficiently strong and safe– material atomic configuration of minimum energy

DAKOTA Optimization MethodsDakota includes Gradient and non-gradient-basedDerivative-free methods methods. Several numerical package areavailable: commercial, developedinternally to Sandia and freesoftware from open-sourcecommunity. Gradient-based methods (DAKOTA will compute finite differencegradients and FD/quasi-Hessians ifnecessary) COLINY (PS, APPS, SolisWets,COBYLA2, EAs, DIRECT)JEGA (single/multi-obj GeneticAlgorithms)EGO (efficient global opt viaGaussian Process models)DIRECT (Gablonsky, Sandiadeveloped)OPT (parallel direct search)DOT (various constrained)CONMIN (CONstrained MINinization) Library:FRCG (Fletcher-Reeves Conjugate Gradient),MFD.NLPQL (SQP, Sequential quadraticprogramming) NLPQL (SQP) OPT (CG, Newton)Calibration (least-squares) NL2SOL (GN QH) NLSSOL (SQP) OPT (Gaussian-Newton)

Considerations when Choosing anOptimization MethodKey considerations: Local and global sensitivity study data; trend and smoothness Simulation expense Constraint types present Goal: local optimization (improvement) or global optimization (best possible)Unconstrained or bound-constrained problems: Smooth and cheap: nearly any method; gradient-based methods will be fastest Smooth and expensive: gradient-based methods Nonsmooth and cheap: non-gradient methods such as pattern search (local opt), genetic algorithms(global opt), DIRECT (global opt), or surrogate-based optimization (quasi local/global opt)Nonsmooth and expensive: surrogate-based optimization (SBO)*Non-linearly-constrained problems: Smooth and cheap: gradient-based methods Smooth and expensive: gradient-based methods Nonsmooth and cheap: non-gradient methods w/ penalty functions, SBO Nonsmooth and expensive: SBO

Scalable ParallelismNested parallel models support large-scale applications and architectures.

User’s Manual:Application Parallelism Use CasesThe parallel computing capabilities provided by DAKOTA are extensive and can bedaunting at first Single-level parallel computing models use: asyncrhronus local, message passing, andhybrid approaches. This method can be combined to build multiple level of parallelism.

Dakota Parallelism, Case 3: Dakota Serial, Tile NProcessor JobsGiven an allocation of M S*N processors, schedule S simultaneous jobsExample: 42 nodes reserved nodes (PLX 1 node 12 procs) , S 21 simultaneousjobs, N 24 processor application runs 1 nodes to run dakota in serialHow would you achieve this?Running dakota in serialasynchronous evaluation concurrency 21Launching application:mpirun -np 24 machinefile simpleFoam -paralleljob scheduler PBS with machinefile listTotal time: residual control on OF, wall time limit for the job

Case 3 Mechanics: Machine File Managementbased When job starts, parse available resource list (e.g., SLURM NODELIST or PBS NODEFILE) into a single list Divide the resources into S files (applicNodeFile.*), each containing N resources For each evaluation, lock a nodefile, run the application using the nodefile, free thenodefile Many variations possible, including specializations where the application size N eitherdivides the number of processors per node or is a multiple of

Standard Dakota Paralellism Standard Dakota implementation, need to wait the completion of a slot ofevaluation concurrency to restart Unused booked computational time, no maximize of the computationalresourcesTImeR22R23R24R36R42End of lastsimulationR1R2R3. . . . . . . . .R15. . . . . . . . .R21Computational resources

Improved Dakota ParalellismImproved Dakota implementation: when an application run completes,need to schedule another job on the freed block of processors,implemented by CINECA's staff Best exploitation of the computational resources. Computational “relay” R26TImeR24R25R23End of lastSimulation, firstconcurrencyR22R2R1R15. . . . . . . . .R23. . . . . . . . .R8Computational resources

Example of Job Submission for Parameter Study42 nodes reserved nodes 1 nodes to run dakota in serial

Example of Input File for Parameter StudyThere are six specification blocks that may appear in DAKOTA input files.

Loosely-coupled loop for DAKOTA in PLXDAKOTAOptimization (example: parametric study,gradient-based method)PBS Job SchedulerCluster of SMP'sDakotaParameters FileDataPre-processingSimulationInput Fileexample.glfDakotaResults FileParametric mesh readable onal Model (simulation)OpenFOAM run-plx.shmpirun -np 48 simpleFoam -parallelSimulationOutput File

Advanced Simulation Code Interfaces: OpenFOAMData pre- and post-processingExample modify the geometry and/or boundary conditions, to optimize acfd quantity Use dprepro to as a parser to modify your input

Advanced Simulation Code Interfaces: OpenFOAM1. Create a template simulation input file by identifying the fields in the giveninput file that correspond to the input in DAKOTA. Example file 0/U,0/U.template2. Use dprepro as parser to reflect names of the DAKOTA parameters filesUz in x13. Insert the change in the loosely-coupled loop4. Change the post-processing section to reflect the revised extractionprocess. Extract your quantity from the output file, with grep command ormore sophisticated extraction tools. Example, extract forces of pressure.outputx1

Simulation Control and quality checkGuidelinesStart with a parametric study to check the influence of the Design of Experimentsvariable Estimate your computational budget Check the single simulation, dakot.out Check the residual of OpenFOAMFor study involving geometrical change, a robust and good quality mesh ismandatory. Use visualization

Check the Quality: Residuals Run Time Visualization of residual implemented by CINECA staff Go to working dir Click one time: Total Residual Click again: Residual on pressure

Bonus SlidesFrequently Asked QuestionsWhy are you releasing DAKOTA as open source?To foster collaborations and streamline the licensing process. Of particular note is the fact thatan export control classification of "publicly available" allows us to work effectively with universities. How is it that Sandia can release government software as open source?Sandia is a government-owned, contractor-operated (GOCO) national laboratory operated forthe U.S. Department of Energy (DOE) by Lockheed Martin Corporation. The authority to releaseopen source software resides with the DOE, and DAKOTA has gone through a series of copyrightassertion and classification approvals to allow release to the general public, (under LGPL).Important proponents for the open source release of Sandia software are the DOE's AcceleratedStrategic Computing (ASC) Program Office and the DOE's Office of Science. Personal noteReminder: Open Source and GPL does not imply zero priceComputer time is still expensive – but cost is unavoidable Software support, help with running and customization is still required Engineers running the code are the most costly part: better!

Optimization (example: parametric study, gradient-based method) Computational Model (simulation) OpenFOAM mpirun -np 48 simpleFoam -parallel example.glf Parametric mesh readable in PointWise Dakota Parameters File Simulation Input File createPatch Simulation Output File Dakota Results File Data Pre-processing Data Post-processing PBS .

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