## **User description** ### **User description** ## Description Adds a numeric method of computing the centroid of IBs where the center of mass is not well posed. In particular, I added hooks for STL and airfiol IBs. This PR also includes support for parameterized IB motion. It allows one to analytically describe the velocity and rotation rate of any IB experiencing 1-way coupling. Both of these features have been tested with IB's the move and rotate using the new analytic parameterization. I have also tested with an airfoil rotating about the correct center of mass. Videos available in my slides. Fixes #1105 Fixes #1106 In addition to these issues being fixed, I also resolved a separate bug that is related in getting the 2-way force calculation to work with multi-fluid flow. I also included some minor refactoring to clean up the time stepper subroutine. ### Type of change Please delete options that are not relevant. - [ ] Bug fix (non-breaking change which fixes an issue) - [ ] New feature (non-breaking change which adds functionality) ### Scope - [ ] This PR comprises a set of related changes with a common goal That goal was enabling the ability to run a pitching airfoil case, which oscillates in time. ## How Has This Been Tested? - [ ] I ran a pitching airfoil case which oscillates in time at a fixed frequency about the new correct center of mass - [ ] I ran a case of a cylinder moving in a circular pattern to "stir" a fluid The best configuration can be summarized with this test case file for the pitching airfoil: ``` import json import math Mu = 1.84e-05 gam_a = 1.4 gam_b = 1.1 total_time = 5.0 num_time_steps = 2000 num_saves = 500 dt = total_time / float(num_time_steps) steps_per_save = int(num_time_steps / num_saves) # Configuring case dictionary print( json.dumps( { # Logistics "run_time_info": "T", # Computational Domain Parameters # axial direction "x_domain%beg": 0.0e00, "x_domain%end": 6.0, # r direction "y_domain%beg": 0.0e00, "y_domain%end": 3.0, "cyl_coord": "F", "m": 400, "n": 200, "p": 0, "dt": dt, "t_step_start": 0, "t_step_stop": num_time_steps, "t_step_save": steps_per_save, # Simulation Algorithm Parameters # Only one patches are necessary, the air tube "num_patches": 1, # Use the 5 equation model "model_eqns": 2, # 6 equations model does not need the K \div(u) term "alt_soundspeed": "F", # One fluids: air "num_fluids": 2, # time step "mpp_lim": "F", # Correct errors when computing speed of sound "mixture_err": "T", # Use TVD RK3 for time marching "time_stepper": 3, # Reconstruct the primitive variables to minimize spurious # Use WENO5 "weno_order": 5, "weno_eps": 1.0e-16, "weno_Re_flux": "T", "weno_avg": "T", "avg_state": 2, "viscous": "T", # Use the mapped WENO weights to maintain monotinicity "mapped_weno": "T", "null_weights": "F", "mp_weno": "T", # Use the HLLC Riemann solver "riemann_solver": 2, "wave_speeds": 1, # We use reflective boundary conditions at octant edges and # non-reflective boundary conditions at the domain edges "bc_x%beg": -3, "bc_x%end": -3, "bc_y%beg": -3, "bc_y%end": -3, # Set IB to True and add 1 patch "ib": "T", "num_ibs": 1, # Formatted Database Files Structure Parameters "format": 1, "precision": 2, "prim_vars_wrt": "T", "E_wrt": "T", "parallel_io": "T", # Patch: Constant Tube filled with air # Specify the cylindrical air tube grid geometry "patch_icpp(1)%geometry": 3, "patch_icpp(1)%x_centroid": 3.0, # Uniform medium density, centroid is at the center of the domain "patch_icpp(1)%y_centroid": 1.5, "patch_icpp(1)%length_x": 6.0, "patch_icpp(1)%length_y": 3.0, # Specify the patch primitive variables "patch_icpp(1)%vel(1)": 3.0e00, "patch_icpp(1)%vel(2)": 0.0e00, "patch_icpp(1)%pres": 1.0e00, "patch_icpp(1)%alpha_rho(1)": 0.8e00, "patch_icpp(1)%alpha(1)": 0.8e00, "patch_icpp(1)%alpha_rho(2)": 0.2e00, "patch_icpp(1)%alpha(2)": 0.2e00, # Patch: Airfoil Immersed Boundary "patch_ib(1)%geometry": 4, "patch_ib(1)%x_centroid": 1.5, "patch_ib(1)%y_centroid": 1.5, "patch_ib(1)%c": 1.0, "patch_ib(1)%t": 0.15, "patch_ib(1)%p": 0.4, "patch_ib(1)%m": 0.02, "patch_ib(1)%angular_vel(3)": "-10.0 * 2.0 * pi * sin(2.0 * pi * t) * pi / 180.", "patch_ib(1)%angles(3)": -5.0 * math.pi / 180., "patch_ib(1)%moving_ibm": 1, "patch_ib(1)%slip": "F", # Fluids Physical Parameters # Use the same stiffness as the air bubble "fluid_pp(1)%gamma": 1.0e00 / (gam_a - 1.0e00), # 2.50(Not 1.40) "fluid_pp(1)%pi_inf": 0, "fluid_pp(1)%Re(1)": 1000000, "fluid_pp(2)%gamma": 1.0e00 / (gam_b - 1.0e00), # 2.50(Not 1.40) "fluid_pp(2)%pi_inf": 0, "fluid_pp(2)%Re(1)": 1000000, } ) ) ``` ## Checklist - [ ] I have added comments for the new code - [ ] I added Doxygen docstrings to the new code - [ ] I have made corresponding changes to the documentation (`docs/`) - [ ] I have added regression tests to the test suite so that people can verify in the future that the feature is behaving as expected - [ ] I have added example cases in `examples/` that demonstrate my new feature performing as expected. They run to completion and demonstrate "interesting physics" - [ ] I ran `./mfc.sh format` before committing my code - [ ] New and existing tests pass locally with my changes, including with GPU capability enabled (both NVIDIA hardware with NVHPC compilers and AMD hardware with CRAY compilers) and disabled - [ ] This PR does not introduce any repeated code (it follows the [DRY](https://en.wikipedia.org/wiki/Don%27t_repeat_yourself) principle) - [ ] I cannot think of a way to condense this code and reduce any introduced additional line count ### If your code changes any code source files (anything in `src/simulation`) To make sure the code is performing as expected on GPU devices, I have: - [ ] Checked that the code compiles using NVHPC compilers - [ ] Checked that the code compiles using CRAY compilers - [ ] Ran the code on either V100, A100, or H100 GPUs and ensured the new feature performed as expected (the GPU results match the CPU results) - [ ] Ran the code on MI200+ GPUs and ensure the new features performed as expected (the GPU results match the CPU results) - [ ] Enclosed the new feature via `nvtx` ranges so that they can be identified in profiles - [ ] Ran a Nsight Systems profile using `./mfc.sh run XXXX --gpu -t simulation --nsys`, and have attached the output file (`.nsys-rep`) and plain text results to this PR - [ ] Ran a Rocprof Systems profile using `./mfc.sh run XXXX --gpu -t simulation --rsys --hip-trace`, and have attached the output file and plain text results to this PR. - [ ] Ran my code using various numbers of different GPUs (1, 2, and 8, for example) in parallel and made sure that the results scale similarly to what happens if you run without the new code/feature ### **PR Type** Enhancement ### **Description** - Add ellipse immersed boundary patch geometry with levelset computation - Implement centroid offset calculation for complex IB shapes (airfoils, STL) - Support analytical parameterization of moving IB velocities and rotation rates - Enable 1-way coupling with analytically-defined IB motion in time-stepping ### Diagram Walkthrough ```mermaid flowchart LR A["IB Patch Definition"] -->|"geometry=6"| B["Ellipse Levelset"] A -->|"centroid_offset"| C["Centroid Computation"] C -->|"airfoil/STL"| D["Center of Mass Calculation"] D -->|"offset vector"| E["Levelset Adjustment"] F["Analytical Parameters"] -->|"vel, angular_vel"| G["1-Way Coupling"] G -->|"time-stepping"| H["IB Motion Update"] ```

File Walkthrough

Relevant files

Enhancement

9 files

m_compute_levelset.fpp `Add ellipse levelset computation and centroid offset`	+60/-1
m_derived_types.fpp `Add centroid offset field to IB patch type`	+1/-0
m_ib_patches.fpp `Add ellipse IB patch initialization and marker setup`	+47/-0
m_check_ib_patches.fpp `Add validation for ellipse IB patch geometry`	+2/-0
m_global_parameters.fpp `Initialize centroid offset to zero for all patches`	+1/-0
m_ibm.fpp `Add centroid offset computation and 1-way coupling support`	+56/-1
m_time_steppers.fpp `Integrate analytical velocity parameterization for 1-way coupling`	+5/-1
case.py `Add code generation for analytical moving IB velocities`	+91/-3
case_dicts.py `Mark IB velocity and angular velocity as analytically-parameterizable`	+2/-4

Documentation

1 files

case.py
Add example case configuration for ellipse IB simulation +97/-0

___ ## **CodeAnt-AI Description** Add analytic moving IB velocities, centroid offset for airfoils, and multi-fluid IB force handling ### What Changed - Immersed boundaries can be driven by analytic (time-dependent) velocity and rotation inputs; the case generator now accepts analytic expressions for IB vel and angular_vel and embeds them into generated input code so 1‑way prescribed IB motion runs without manual code edits. - For irregular IB shapes (NACA airfoils, STL, ellipses) the code computes the true center of mass at startup and applies a centroid offset so rotations and positions use the physically correct center rather than the input "centroid". - IB force calculation now supports multiple fluids: pressure and viscous contributions are computed per-fluid, the local dynamic viscosity is weighted by local phase fraction, and Reynolds-number handling avoids divide-by-zero for zero-Re cases. - Time-step handling for moving IBs was refactored so IB propagation (analytic motion, two‑way forcing, rotation, and position updates) is centralized and ensures forces are computed once per stage when needed. ### Impact `✅ Can run pitching or rotating airfoils about correct center` `✅ Clearer analytic IB motion setup in generated case files` `✅ Correct IB forces for multi-fluid viscous flows`

💡 Usage Guide

### Checking Your Pull Request Every time you make a pull request, our system automatically looks through it. We check for security issues, mistakes in how you're setting up your infrastructure, and common code problems. We do this to make sure your changes are solid and won't cause any trouble later. ### Talking to CodeAnt AI Got a question or need a hand with something in your pull request? You can easily get in touch with CodeAnt AI right here. Just type the following in a comment on your pull request, and replace "Your question here" with whatever you want to ask:

@codeant-ai ask: Your question here

This lets you have a chat with CodeAnt AI about your pull request, making it easier to understand and improve your code. #### Example

@codeant-ai ask: Can you suggest a safer alternative to storing this secret?

### Preserve Org Learnings with CodeAnt You can record team preferences so CodeAnt AI applies them in future reviews. Reply directly to the specific CodeAnt AI suggestion (in the same thread) and replace "Your feedback here" with your input:

@codeant-ai: Your feedback here

This helps CodeAnt AI learn and adapt to your team's coding style and standards. #### Example

@codeant-ai: Do not flag unused imports.

### Retrigger review Ask CodeAnt AI to review the PR again, by typing:

@codeant-ai: review

### Check Your Repository Health To analyze the health of your code repository, visit our dashboard at [https://app.codeant.ai](https://app.codeant.ai). This tool helps you identify potential issues and areas for improvement in your codebase, ensuring your repository maintains high standards of code health.

## Summary by CodeRabbit * **New Features** * Ellipse-shaped immersed boundary patches supported * Centroid-offset correction improves handling of irregular immersed boundaries * Analytical moving immersed boundaries (prescribed MIB motion) supported * Multi‑fluid immersed boundary interactions and per‑fluid viscous handling * **Chores** * Consolidated immersed-boundary propagation during time stepping and minor example/comment updates _{✏️ Tip: You can customize this high-level summary in your review settings.}