# SimPEG.electromagnetics.time_domain.Simulation3DMagneticFluxDensity#

class SimPEG.electromagnetics.time_domain.Simulation3DMagneticFluxDensity(mesh, survey=None, dt_threshold=1e-08, **kwargs)[source]#

Starting from the quasi-static E-B formulation of Maxwell’s equations (semi-discretized)

$\begin{split}\mathbf{C} \mathbf{e} + \frac{\partial \mathbf{b}}{\partial t} = \mathbf{s_m} \\ \mathbf{C}^{\top} \mathbf{M_{\mu^{-1}}^f} \mathbf{b} - \mathbf{M_{\sigma}^e} \mathbf{e} = \mathbf{s_e}\end{split}$

where $$\mathbf{s_e}$$ is an integrated quantity, we eliminate $$\mathbf{e}$$ using

$\mathbf{e} = \mathbf{M_{\sigma}^e}^{-1} \mathbf{C}^{\top} \mathbf{M_{\mu^{-1}}^f} \mathbf{b} - \mathbf{M_{\sigma}^e}^{-1} \mathbf{s_e}$

to obtain a second order semi-discretized system in $$\mathbf{b}$$

$\mathbf{C} \mathbf{M_{\sigma}^e}^{-1} \mathbf{C}^{\top} \mathbf{M_{\mu^{-1}}^f} \mathbf{b} + \frac{\partial \mathbf{b}}{\partial t} = \mathbf{C} \mathbf{M_{\sigma}^e}^{-1} \mathbf{s_e} + \mathbf{s_m}$

and moving everything except the time derivative to the rhs gives

$\frac{\partial \mathbf{b}}{\partial t} = -\mathbf{C} \mathbf{M_{\sigma}^e}^{-1} \mathbf{C}^{\top} \mathbf{M_{\mu^{-1}}^f} \mathbf{b} + \mathbf{C} \mathbf{M_{\sigma}^e}^{-1} \mathbf{s_e} + \mathbf{s_m}$

For the time discretization, we use backward euler. To solve for the $$n+1$$ th time step, we have

$\frac{\mathbf{b}^{n+1} - \mathbf{b}^{n}}{\mathbf{dt}} = -\mathbf{C} \mathbf{M_{\sigma}^e}^{-1} \mathbf{C}^{\top} \mathbf{M_{\mu^{-1}}^f} \mathbf{b}^{n+1} + \mathbf{C} \mathbf{M_{\sigma}^e}^{-1} \mathbf{s_e}^{n+1} + \mathbf{s_m}^{n+1}$

re-arranging to put $$\mathbf{b}^{n+1}$$ on the left hand side gives

$(\mathbf{I} + \mathbf{dt} \mathbf{C} \mathbf{M_{\sigma}^e}^{-1} \mathbf{C}^{\top} \mathbf{M_{\mu^{-1}}^f}) \mathbf{b}^{n+1} = \mathbf{b}^{n} + \mathbf{dt}(\mathbf{C} \mathbf{M_{\sigma}^e}^{-1} \mathbf{s_e}^{n+1} + \mathbf{s_m}^{n+1})$

Methods

 Fields_Derivs fieldsPair getAdiag(tInd) System matrix at a given time index getAdiagDeriv(tInd, u, v[, adjoint]) Derivative of ADiag getAsubdiag(tInd) Matrix below the diagonal getRHS(tInd) Assemble the RHS getRHSDeriv(tInd, src, v[, adjoint]) Derivative of the RHS
 getAsubdiagDeriv

## Galleries and Tutorials using SimPEG.electromagnetics.time_domain.Simulation3DMagneticFluxDensity#

EM: TDEM: Permeable Target, Inductive Source

EM: TDEM: Permeable Target, Inductive Source

EM: TDEM: 1D: Inversion with VTEM waveform

EM: TDEM: 1D: Inversion with VTEM waveform

Heagy et al., 2017 1D FDEM and TDEM inversions

Heagy et al., 2017 1D FDEM and TDEM inversions

Forward Simulation Including Inductive Response

Forward Simulation Including Inductive Response

3D Forward Simulation for Transient Response on a Cylindrical Mesh

3D Forward Simulation for Transient Response on a Cylindrical Mesh

3D Forward Simulation with User-Defined Waveforms

3D Forward Simulation with User-Defined Waveforms