How exactly is the Center of Mass caculated in eel2d?

[X A]

Hi,

It is a beginner problem.

I am trying to understand how the Center of Mass (COM) is calculated in eel2d case.

So we can see it is done by this line:

std::vector<std::vector<double> > structure_COM = ib_method_ops->getCurrentStructureCOM();

https://github.com/IBAMR/IBAMR/blob/ba414b413c14a8cd006781aa26832994c689fdba/examples/ConstraintIB/eel2d/example.cpp#L237

Tracing "getCurrentStructureCOM();"

It comes from the header file:

https://github.com/IBAMR/IBAMR/blob/b1eee5a913d962f286d16dc98b4399148d27b978/include/ibamr/ConstraintIBMethod.h#L205

inline const std::vector<std::vector<double> >& getCurrentStructureCOM()
{
return d_center_of_mass_current;
}  

I tried to find how it is calculated:

$ grep -r -i d_center_of_mass_current . ./ibamr/IBAMR/include/ibamr/BrinkmanPenalizationRigidBodyDynamics.h: return d_center_of_mass_current; ./ibamr/IBAMR/include/ibamr/BrinkmanPenalizationRigidBodyDynamics.h: d_center_of_mass_current = Eigen::Vector3d::Zero(), d_center_of_mass_new = Eigen::Vector3d::Zero(); ./ibamr/IBAMR/include/ibamr/CIBStrategy.h: IBTK::EigenAlignedVector<Eigen::Vector3d> d_center_of_mass_initial, d_center_of_mass_current, d_center_of_mass_half, ./ibamr/IBAMR/include/ibamr/ConstraintIBMethod.h: return d_center_of_mass_current; ./ibamr/IBAMR/include/ibamr/ConstraintIBMethod.h: std::vector<std::vector<double> > d_center_of_mass_current, d_center_of_mass_new; ./ibamr/IBAMR/include/ibamr/IBFEDirectForcingKinematics.h: return d_center_of_mass_current; ./ibamr/IBAMR/include/ibamr/IBFEDirectForcingKinematics.h: d_center_of_mass_current = Eigen::Vector3d::Zero(), d_center_of_mass_half = Eigen::Vector3d::Zero(), ./ibamr/IBAMR/include/ibamr/IBInterpolantMethod.h: IBTK::EigenAlignedVector<Eigen::Vector3d> d_center_of_mass_initial, d_center_of_mass_current, d_center_of_mass_new; ./ibamr/IBAMR/src/IB/BrinkmanPenalizationRigidBodyDynamics.cpp: d_center_of_mass_current = X_com; ./ibamr/IBAMR/src/IB/BrinkmanPenalizationRigidBodyDynamics.cpp: d_center_of_mass_new = d_center_of_mass_current; ./ibamr/IBAMR/src/IB/BrinkmanPenalizationRigidBodyDynamics.cpp: d_center_of_mass_new = d_center_of_mass_current + dt * d_trans_vel_new; ./ibamr/IBAMR/src/IB/BrinkmanPenalizationRigidBodyDynamics.cpp: d_center_of_mass_current = d_center_of_mass_new; ./ibamr/IBAMR/src/IB/BrinkmanPenalizationRigidBodyDynamics.cpp: db->putDoubleArray(C, &d_center_of_mass_current[0], 3); ./ibamr/IBAMR/src/IB/BrinkmanPenalizationRigidBodyDynamics.cpp: db->getDoubleArray(C, &d_center_of_mass_current[0], 3); ./ibamr/IBAMR/src/IB/CIBMethod.cpp: d_center_of_mass_current = d_center_of_mass_new; ./ibamr/IBAMR/src/IB/CIBMethod.cpp: d_center_of_mass_current = d_center_of_mass_initial; ./ibamr/IBAMR/src/IB/CIBMethod.cpp: X_half[d] = d_center_of_mass_current[struct_handle][d] + R_dr[d] + ./ibamr/IBAMR/src/IB/CIBMethod.cpp: d_center_of_mass_current[struct_no][d] + 0.5 * dt * d_trans_vel_current[struct_no][d]; ./ibamr/IBAMR/src/IB/CIBMethod.cpp: d_center_of_mass_current[struct_handle][d] + R_dr[d] + ./ibamr/IBAMR/src/IB/CIBMethod.cpp: Eigen::Vector3d& current_com = d_center_of_mass_current[struct_no]; ./ibamr/IBAMR/src/IB/CIBMethod.cpp: db->putDoubleArray("C_" + struct_no_str, &d_center_of_mass_current[struct_no][0], 3); ./ibamr/IBAMR/src/IB/CIBMethod.cpp: db->getDoubleArray("C_" + struct_no_str, &d_center_of_mass_current[struct_no][0], 3); ./ibamr/IBAMR/src/IB/CIBStrategy.cpp: d_center_of_mass_current.resize(d_num_rigid_parts, Eigen::Vector3d::Zero()); ./ibamr/IBAMR/src/IB/CIBStrategy.cpp: return d_center_of_mass_current[part]; ./ibamr/IBAMR/src/IB/ConstraintIBMethod.cpp: d_center_of_mass_current(d_no_structures, std::vector<double>(3, 0.0)), ./ibamr/IBAMR/src/IB/ConstraintIBMethod.cpp: db->putDoubleArray("POSN_COM_STRUCT_" + struct_no_str, &d_center_of_mass_current[struct_no][0], 3); ./ibamr/IBAMR/src/IB/ConstraintIBMethod.cpp: db->getDoubleArray("POSN_COM_STRUCT_" + struct_no_str, &d_center_of_mass_current[struct_no][0], 3); ./ibamr/IBAMR/src/IB/ConstraintIBMethod.cpp: d_center_of_mass_current[struct_no], ./ibamr/IBAMR/src/IB/ConstraintIBMethod.cpp: d_center_of_mass_current[struct_no][d] = 0.0; ./ibamr/IBAMR/src/IB/ConstraintIBMethod.cpp: d_center_of_mass_current[struct_no][i] = d_center_of_mass_unshifted_current[struct_no][i]; ./ibamr/IBAMR/src/IB/ConstraintIBMethod.cpp: while (d_center_of_mass_current[struct_no][i] < domain_x_lower[i]) ./ibamr/IBAMR/src/IB/ConstraintIBMethod.cpp: d_center_of_mass_current[struct_no][i] += domain_length[i]; ./ibamr/IBAMR/src/IB/ConstraintIBMethod.cpp: while (d_center_of_mass_current[struct_no][i] >= domain_x_upper[i]) ./ibamr/IBAMR/src/IB/ConstraintIBMethod.cpp: d_center_of_mass_current[struct_no][i] -= domain_length[i]; ./ibamr/IBAMR/src/IB/ConstraintIBMethod.cpp: << d_FuRMoRP_current_time << '\t' << d_center_of_mass_current[struct_no][0] << '\t' ./ibamr/IBAMR/src/IB/ConstraintIBMethod.cpp: << d_center_of_mass_current[struct_no][1] << '\t' << d_center_of_mass_current[struct_no][2] ./ibamr/IBAMR/src/IB/ConstraintIBMethod.cpp: X_half[d] = d_center_of_mass_current[location_struct_handle][d] + ./ibamr/IBAMR/src/IB/ConstraintIBMethod.cpp: X_new[d] = d_center_of_mass_current[location_struct_handle][d] + ./ibamr/IBAMR/src/IB/IBFEDirectForcingKinematics.cpp: d_center_of_mass_current = d_center_of_mass_initial; ./ibamr/IBAMR/src/IB/IBFEDirectForcingKinematics.cpp: d_center_of_mass_current[d] + Rxdr_half[d] + 0.5 * dt * d_trans_vel_current[d]); ./ibamr/IBAMR/src/IB/IBFEDirectForcingKinematics.cpp: d_center_of_mass_current[d] + Rxdr_new[d] + dt * d_trans_vel_current[d]); ./ibamr/IBAMR/src/IB/IBFEDirectForcingKinematics.cpp: d_center_of_mass_half = d_center_of_mass_current + 0.5 * dt * d_trans_vel_current; ./ibamr/IBAMR/src/IB/IBFEDirectForcingKinematics.cpp: d_center_of_mass_new = d_center_of_mass_current + dt * d_trans_vel_current; ./ibamr/IBAMR/src/IB/IBFEDirectForcingKinematics.cpp: X_half_petsc.set(nodal_X_indices[d][k], d_center_of_mass_current[d] + Rxdr[d] + dt * d_trans_vel_half[d]); ./ibamr/IBAMR/src/IB/IBFEDirectForcingKinematics.cpp: d_center_of_mass_half = d_center_of_mass_current + dt * d_trans_vel_half; ./ibamr/IBAMR/src/IB/IBFEDirectForcingKinematics.cpp: d_center_of_mass_current = d_center_of_mass_new; ./ibamr/IBAMR/src/IB/IBFEDirectForcingKinematics.cpp: db->putDoubleArray("C", &d_center_of_mass_current[0], 3); ./ibamr/IBAMR/src/IB/IBFEDirectForcingKinematics.cpp: db->getDoubleArray("C", &d_center_of_mass_current[0], 3); ./ibamr/IBAMR/src/IB/IBInterpolantMethod.cpp: d_center_of_mass_current.resize(d_num_rigid_parts, Eigen::Vector3d::Zero()); ./ibamr/IBAMR/src/IB/IBInterpolantMethod.cpp: d_center_of_mass_current = d_center_of_mass_new; ./ibamr/IBAMR/src/IB/IBInterpolantMethod.cpp: X_new[d] = d_center_of_mass_current[struct_handle][d] + R_dr[d] + dt * U[struct_handle][d]; ./ibamr/IBAMR/src/IB/IBInterpolantMethod.cpp: d_center_of_mass_new[struct_no][d] = d_center_of_mass_current[struct_no][d] + dt * U[struct_no][d]; ./ibamr/IBAMR/src/IB/IBInterpolantMethod.cpp: d_center_of_mass_current = d_center_of_mass_initial; ./ibamr/IBAMR/src/IB/IBInterpolantMethod.cpp: db->putDoubleArray(C.str(), &d_center_of_mass_current[struct_no][0], 3); ./ibamr/IBAMR/src/IB/IBInterpolantMethod.cpp: db->getDoubleArray(C.str(), &d_center_of_mass_current[struct_no][0], 3);

But still it seems it is often used, but I just could not find where it is calculated (would expect something like Volume integration).

So I would just like to enquire how to trace the actual calculation of COM. The method may also be important to understand other parts of the library.

I am now just trying to piece everything together in the gdb debugger, but I do not know if it will work.

Appreciate any comment.

With best wishes,

Mike

[Boyce Griffith]

Take a look at ConstraintIBMethod::calculateCOMandMOIOfStructures().

So I would just like to enquire how to trace the actual calculation of COM. The method may also be important to understand other parts of the library.

I am now just trying to piece everything together in the gdb debugger, but I do not know if it will work.

Appreciate any comment.

With best wishes,

Mike

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[X A]

Thank you very much!

Mike