comsol

name comsol description General-purpose COMSOL Multiphysics automation via the mph Python library and COMSOL Java API. Use when the user needs to: (1) Create COMSOL models programmatically (geometry, materials, physics, multiphysics, mesh, probes), (2) Set up and run parametric/time-domain/frequency studies, (3) Extract and export simulation results (probe data, field evaluations, cut points), (4) Debug COMSOL API calls or model-tree navigation, (5) Work with .mph files from Python. Covers COMSOL versions 6.0–6.3 on Windows/Linux/macOS with mph stand-alone and client-server modes. All API patterns verified against COMSOL 6.2 via live testing. Self-improves by logging debugging discoveries to references/debugging-log.md. compatibility Requires COMSOL Multiphysics 6.0–6.3, mph Python library, numpy, pandas. Stand-alone mode only on Windows. Linux/macOS require client-server mode. metadata {"version":"1.2.0","comsol_version":"6.2"} COMSOL Automation via mph Use the mph Python library to control COMSOL programmatically. Always prefer the Java API bridge ( model.java ) over mph's Python wrapper for physics/material/mesh/study/probe setup — the mph Python API is mainly for parameters, geometry, saving, and solving. Prerequisites & auto-detection Required : COMSOL Multiphysics 6.0–6.3 installed (any license type) Python 3.x 64-bit (NOT Microsoft Store version on Windows) pip install mph numpy pandas Auto-detection : mph finds COMSOL automatically via Windows registry (Windows), default install paths, or the comsol command in PATH. No manual path config needed. mph.discovery.backend() returns the install root — use this to locate comsolbatch too (see Solving section below). If COMSOL not installed : mph.start() raises an error. Check: Windows: C:\Program Files\COMSOL\COMSOL6*\Multiphysics\bin\win64\comsol.exe Linux: /usr/local/comsol*/multiphysics/bin/glnxa64/comsol macOS: /Applications/COMSOL*/Multiphysics/bin/maci64/comsol If mph not installed : ModuleNotFoundError: No module named 'mph' → pip install mph Quick-start checklist pip install mph numpy pandas mph.option('session', 'stand-alone') on Windows (fastest) client = mph.start(cores=N) → pymodel = client.create('Name') Access the Java bridge: model = pymodel.java Build the model using the patterns below Save: pymodel.save('file.mph') Solve: pymodel.solve() Extract data and export Essential API patterns (all discovered via live testing against COMSOL 6.2) Model structure — ALWAYS create the component explicitly model.modelNode().create( "comp1" ) # required BEFORE any geometry model.geom().create( "geom1" , 3 ) # 3D geometry model.geom( "geom1" ).feature().create( "blk1" , "Block" ) model.geom( "geom1" ).feature( "blk1" ). set ( "size" , [ "Lx" , "Ly" , "Lz" ]) model.geom( "geom1" ).run( "fin" ) comp = model.component( "comp1" ) # now accessible Critical : model.component("comp1") only works after modelNode().create("comp1") . Do NOT mix mph Python geometry creation with Java API — choose one path and stick to it. Global parameters model.param(). set ( "Lx" , "40 [mm]" ) model.param(). set ( "T_amb" , "293.15 [K]" ) Material properties — MUST use propertyGroup('def') mat = comp.material().create( "mat1" , "Common" ) mat.label( "My Material" ) mat.selection(). all () grp = mat.propertyGroup( "def" ) grp. set ( "density" , "2700 [kg/m^3]" ) grp. set ( "youngsmodulus" , "69e9 [Pa]" ) grp. set ( "poissonsratio" , "0.33" ) grp. set ( "thermalconductivity" , "167 [W/(m*K)]" ) grp. set ( "heatcapacity" , "896 [J/(kg*K)]" ) grp. set ( "thermalexpansioncoefficient" , "23.6e-6 [1/K]" ) Critical : NEVER use mat.set(prop, val) — it will fail. ALWAYS go through mat.propertyGroup("def").set(prop, val) . Physics interfaces — verified tags for COMSOL 6.2 Desired physics Correct Java tag Via Heat Transfer in Solids "HeatTransfer" comp.physics().create("ht", "HeatTransfer", "geom1") Solid Mechanics "SolidMechanics" comp.physics().create("solid", "SolidMechanics", "geom1") Thermal Expansion (multiphysics) "ThermalExpansion" comp.multiphysics().create("te1", "ThermalExpansion", "geom1") Wrong tags that will FAIL : "HeatTransferInSolids" , "HeatTransferSolids" , "StructuralMechanics" , "Solid" . Boundary condition features — verified tags Feature Tag Dimension Boundary heat source (laser) "BoundaryHeatSource" 2 (3D boundary) Low-reflecting boundary "LowReflectingBoundary" 2 (3D boundary) Wrong tags that will FAIL : "HeatFlux" , "InwardHeatFlux" , "AbsorbingBoundary" . Selections — prefer direct entity numbers Named selections via feature.selection().set("name") FAILS in client API. Use .named("name") for mesh features or direct entity numbers for physics: # Physics features: direct entity numbers (MUST use jpype.JArray) bhs.selection(). set (jpype.JArray(jpype.JInt, 1 )([ 6 ])) # boundary 6 = top # Mesh Size features: named selection via .named() (NOT .set()) size_fine.selection().named( "sel_wave_region" ) # Ball selection for mesh refinement (entitydim is STRING, radius is "r") fine_sel = comp.selection().create( "sel_wave_region" , "Ball" ) fine_sel. set ( "entitydim" , "3" ) # string "3", not int 3! fine_sel. set ( "posx" , "x0" ) fine_sel. set ( "posy" , "y0" ) fine_sel. set ( "posz" , "Lz/2" ) fine_sel. set ( "r" , "r_coarse" ) # "r" not "radius"! Mesh — Size nodes and FreeTet mesh = comp.mesh().create( "mesh1" ) mesh.feature( "size" ). set ( "hmax" , "h_coarse" ) mesh.feature( "size" ). set ( "hmin" , "0.01 [mm]" ) # Local refinement (Ball selection, entitydim string, r not radius) fine = mesh.feature().create( "size_fine" , "Size" ) fine. set ( "hmax" , "h_fine" ) fine_sel = comp.selection().create( "sel_fine" , "Ball" ) fine_sel. set ( "entitydim" , "3" ) # STRING! fine_sel. set ( "posx" , "x0" ) fine_sel. set ( "posy" , "y0" ) fine_sel. set ( "posz" , "Lz/2" ) fine_sel. set ( "r" , "r_coarse" ) # "r" NOT "radius"! fine.selection().named( "sel_fine" ) # .named() NOT .set()! mesh.feature().create( "ftet1" , "FreeTet" ) mesh.run() Data extraction — use pymodel.evaluate() + nearest-node CutPoint3D + res.numerical() does not work via the client API. Instead, evaluate the full field and find nearest mesh nodes: import numpy as np # Get node coordinates at t=0 x0 = pymodel.evaluate( "x" , "mm" ) # (n_timesteps, n_nodes) coords = np.column_stack([x0[ 0 ], pymodel.evaluate( "y" , "mm" )[ 0 ], pymodel.evaluate( "z" , "mm" )[ 0 ]]) # Full displacement field w_all = pymodel.evaluate( "w" , "mm" ) # (n_timesteps, n_nodes) # Nearest-node lookup for each target point for pt in target_points: dists = np.linalg.norm(coords - [pt[ "x" ], pt[ "y" ], pt[ "z" ]], axis= 1 ) nearest = np.argmin(dists) time_series = w_all[:, nearest] # extract this node's time series Time-dependent study study = model.study().create( "std1" ) step = study.feature().create( "time" , "Transient" ) step. set ( "tlist" , "range(0, 5e-9, 10e-6)" ) step. set ( "rtol" , "1e-5" ) Thermal Expansion — add to Linear Elastic Material (NOT multiphysics) The comp.multiphysics().create("te1","ThermalExpansion") node cannot be configured via the client API (its ThermalExpansionModel sub-feature reports "Unknown feature ID"). Instead, add ThermalExpansion as a sub-feature of the Solid Mechanics Linear Elastic Material node: lemm = solid.feature( "lemm1" ) # Linear Elastic Material tef = lemm.feature().create( "tef1" , "ThermalExpansion" ) tef. set ( "Tref" , "T_amb" ) # reference temperature tef. set ( "alpha" , "23.6e-6 [1/K]" ) # CTE exp() underflow — keep denominator > 1e-5 Gaussian expressions like exp(-r²/(2*sigma_s²)) evaluate to zero globally if the denominator D = 2*sigma_s² is ≤ 1e-5. At far mesh nodes exp(-r²/D) underflows to 0, and COMSOL then zeros the entire expression. Rule : Ensure D > 5e-5 (sigma_s ≥ 5 mm). For a plate of size X by Y, the max distance from center is r_max = sqrt((X/2)²+(Y/2)²) , and you need r_max²/D < ~40 to avoid underflow. Also broken via API: max() , min() , if() , and spatial comparisons like ((x-x0)² < 2*sigma_s²) — all evaluate to 0 on boundaries. Solving: use mph.solve() (comsolbatch drops solution data) comsolbatch does NOT save solution datasets to the output .mph file, making post-solve data extraction impossible. Use pymodel.solve() instead. mph stand-alone mode runs in a headless JVM (no Swing GUI), so the COMSOL progress window won't appear. For progress monitoring during long solves, use --build-only first, then solve interactively in COMSOL Desktop. Build phase (mph, always fast) python laser_ultrasound_model.py --build-only Solve phase (mph) pymodel.solve() # blocking, solution data preserved File lock workaround pymodel.save("name.mph") fails if the filename was used earlier in the same session. Save with a UUID suffix: import uuid pre_solve_name = f"_pre_solve_ {uuid.uuid4(). hex [: 8 ]} .mph" pymodel.save(pre_solve_name) Output looks like: Time-step 1, Nonlinear iterations: 2, Convergence: 1.2e-6 Time-step 2, Nonlinear iterations: 1, Convergence: 8.3e-7 ... Post-solve (mph, data extraction) client = mph.start(cores= 4 ) model = client.load( str (output_dir / "solved_model.mph" )) # Then use CutPoint3D / result().numerical() to extract data Alternative: solve in COMSOL Desktop GUI Open the .mph in COMSOL Desktop → Study → Compute. Full progress window with convergence plots, real-time probe graphs, and solver log. Common pitfalls & fallbacks mph.start() stand-alone fails → switch to mph.option('session', 'client-server') Physics tag unknown → check references/api-reference.md for verified tags mat.set() fails → MUST use mat.propertyGroup("def").set(prop, val) model.component("comp1") fails → modelNode().create("comp1") must be called first set("entitydim", 2) ambiguous → pass as string: set("entitydim", "2") set("radius", ...) unknown → use "r" not "radius" selection().set("name") → use .named("name") for named, .set(JArray([N])) for nums BoxSelection / BallSelection unknown → drop Selection suffix: "Box" , "Ball" DomainPointProbe fails → use result().dataset().create("cpt", "CutPoint3D") post-solve selection().all() on free1 → Free BC is read-only, skip it