Improved Algorithms: Pressure Calculation

Table of Contents

• Pressure Calculation Methods
• How It's Switched
  • Input
  • Loading
  • Assigning the Class
  • Pressure Calculation

Pressure Calculation Methods

• Implicit
• Explicit

How It's Switched

Let's take a look at how the pressure calculation method is being modified.

Input

First, we specify which method to use in settings.yml:

# pressure calculation method
pressureCalculationMethod: Implicit # Implicit or Explicit
# for Implicit
compressibility: 0.45e-09
relaxationCoefficientForPressure: 0.2
# for Explicit
soundSpeed: 17.1

Loading

When executing the program, the location of settings.yml is passed through the --setting argument. Then main() function initiates Simulation class:

int main(int argc, char** argv) {
    // -----
    // -----
    // -----
 
    auto settingPath     = fs::path(program.get<std::string>("--setting"));
    auto outputDirectory = fs::path(program.get<std::string>("--output"));
    Simulation simulation(settingPath, outputDirectory);
    simulation.run();
 
    return 0;
}

Simulation::Simulation() receives settingPath, and make Loader load settings.yml. User-defined pressure calculation method is now set in input.settings.pressureCalculationMethod.

Simulation::Simulation(fs::path& settingPath, fs::path& outputDirectory) {
    Input input = loader.load(settingPath, outputDirectory);
 
    // -----
    // -----
    // -----
}

Assigning the Class

Then it moves on to switching the pressure method. This part consists of three steps.

1. Create PressureCalculator::Interface class variable named pressureCalculator.
2. User-specified Pressure Calculator class (Implicit, Explicit, ...) will be assigned to the pressureCalculator variable, using if statements.
3. pressureCalculator will be handed over to MPS::MPS(), the constructor of MPS class. Inside MPS::MPS(), pressureCalculator will be copied to it's own public attributes.

Simulation::Simulation(fs::path& settingPath, fs::path& outputDirectory) {
    // -----
    // -----
    // -----
 
    std::unique_ptr<PressureCalculator::Interface> pressureCalculator;
    if (input.settings.pressureCalculationMethod == "Implicit") {
        pressureCalculator.reset(
          new PressureCalculator::Implicit(
            // arguments for constructor
        ));
 
    } else if (input.settings.pressureCalculationMethod == "Explicit") {
        pressureCalculator.reset(
          new PressureCalculator::Explicit(
            // arguments for constructor
        ));
    }
 
    mps = MPS(input, std::move(pressureCalculator));
 
    // -----
    // -----
    // -----
}

Note

Here we use "Interface Class" and "Smart Pointer". See Coding Techniques for more information.

Pressure Calculation

Finally, at each time step, MPS::stepForward() calls pressureCalculator that MPS class maintains, and execute pressure calculation.

void MPS::stepForward() {
    // -----
    // -----
    // -----
 
    auto pressures = pressureCalculator->calc(particles);
    for (auto& particle : particles) {
        particle.pressure = pressures[particle.id];
    }
 
    // -----
    // -----
    // -----
}