Warning

The API of the classes probably will change in the future. It is a first draft implementation to iterate over the design.

Boundary Conditions

In contrast to OpenFOAM, the boundary conditions do not store the underlying data but instead modify the data provided by Field. A basic NoOp implementation is provided by the VolumeBoundary and SurfaceBoundary classes. To apply boundary conditions for both Surface and Volume Vectors, a virtual base class member function correctBoundaryConditions is used. The member acts as an interface and is responsible for updating the actual boundary data contained within an InternalVector (an attribute of the Field).

template<typename ValueType>
class VolumeBoundary : public NeoN::finiteVolume::cellCentred::BoundaryPatchMixin

Represents a volume boundary field for a cell-centered finite volume method.

Template Parameters:

ValueType – The data type of the field.

template<typename ValueType>
class SurfaceBoundary : public NeoN::finiteVolume::cellCentred::BoundaryPatchMixin

Represents a surface boundary field for a cell-centered finite volume method.

Template Parameters:

ValueType – The data type of the field.

The above are the base classes for the specific (derived) implementations which will ultimately provide the actual boundary conditions to both volumetric and surface fields.

Boundary Conditions for VolumeVector’s

The function correctBoundaryConditions is responsible for modifying the data of the boundaryVector using the visitor pattern. A possible implementation is shown below.

void fvccScalarFixedValueBoundaryVector::correctBoundaryConditions(
    BoundaryData<scalar>& bfield, const Vector<scalar>& internalVector
)
{
    fixedValueBCKernel kernel_(mesh_, patchID_, start_, end_, uniformValue_);
    std::visit([&](const auto& exec) { kernel_(exec, bfield, internalVector); }, bfield.exec());
}

The logic is implemented in the kernel classes:

void fixedValueBCKernel::operator()(
    const GPUExecutor& exec, BoundaryData<scalar>& bVector, const Vector<scalar>& internalVector
)
{
    using executor = typename GPUExecutor::exec;
    auto s_value = bVector.value().field();
    auto s_refValue = bVector.refValue().field();
    scalar uniformValue = uniformValue_;
    Kokkos::parallel_for(
        "fvccScalarFixedValueBoundaryVector",
        Kokkos::RangePolicy<executor>(start_, end_),
        KOKKOS_LAMBDA(const size_t i) {
            s_value[i] = uniformValue;
            s_refValue[i] = uniformValue;
        }
    );
}

As the BoundaryData class stores all data in a contiguous array, the boundary condition must only update the data in the range of the boundary specified by the start_ and end_ index. In the above simple boundary condition, the kernel only sets the values to a uniform/fixed value. The value field stores the current value of the boundary condition that is used by the explicit operators and the refValue stores the value of the boundary condition that is used by the implicit operators.

Currently, the following boundary conditions are implemented for volVector for scalar: - fixedValue - zeroGradient - calculated