# Kratos Magnetostatic Application

(Difference between revisions)
 Revision as of 16:05, 1 February 2010 (view source)JMora (Talk | contribs) (New page: == General Description == The KRATOS Electrostatic Application deals with the Finite Element Analysis of problems in [http://en.wikipedia.org/wiki/Electrostatics '''electrosta...) Latest revision as of 11:12, 12 January 2011 (view source)JMora (Talk | contribs) (19 intermediate revisions by 2 users not shown) Line 1: Line 1: == General Description == == General Description == − The [[Kratos | KRATOS]] Electrostatic Application deals with the Finite Element Analysis of problems in [http://en.wikipedia.org/wiki/Electrostatics '''electrostatics''']. It can be considered the most basic problem in [http://en.wikipedia.org/wiki/Electromagnetism electromagnetism] and it use to be the first chapter in the introductory books about electromagnetism. + The [[Kratos | KRATOS]] Magnetostatic Application deals with the Finite Element Analysis of problems in [http://en.wikipedia.org/wiki/Magnetostatics '''magnetostatics''']. Though the mathematics and general formulation is quite similar to Electrostatics, Magnetostatics presents important differences at a conceptual and a programming level. Therefore, if you are a beginner in electromagnetism or programming electromagnetic applications, we strongly recommend you that you first start with the [[Kratos_Electrostatic_Application |Electrostatic application]]. − Therefore, the following description of the '''Kratos Electrostatic Application''' can be used as an introduction to: + The following description of the '''Kratos Magnetostatic Application''' takes part of: * general concepts in [http://en.wikipedia.org/wiki/Electromagnetism '''electromagnetism''']; * general concepts in [http://en.wikipedia.org/wiki/Electromagnetism '''electromagnetism''']; * the [http://en.wikipedia.org/wiki/Finite_element_method '''Finite Element Method'''] applied to the electromagnetism; * the [http://en.wikipedia.org/wiki/Finite_element_method '''Finite Element Method'''] applied to the electromagnetism; * the use of Kratos for basic problems; * the use of Kratos for basic problems; + At a first glance, it could be said that Electrostatics works with static charges whereas Magnetostatics does it with dynamic charges (or [http://en.wikipedia.org/wiki/Electric_current static currents]). That's partially true and we avoid by now to argue about it. On the opposite, we are going to consider Magnetostatics as a completely new phenomenon instead of thinking in a kind of 'dynamic' electrostatic. − + − + − Electrostatic establishes the most basic principles of the Maxwell equations and it is excellent to work at academic level. Nevertheless, some serious industrial applications can be solved by using just these simplest equations and simulation program (circuit components such as condensers and bipolar diodes, electrical field distribution for high voltage systems, etc). + == Theory == == Theory == − Magnetostatics refers to the physical phenomena related to the presence of electric charges in the objects. + Magnetostatics refers to the physical phenomena related to the presence of stationary electric currents in the objects (magnetic materials can be considered as those with internal microcurrents). That means that we ignore any electrostatic charge, the electric field and we presume a constant magnetic field with respect to time. === Basic principles === === Basic principles === − ::[[Image:Cargas.jpg]] + − Our first Maxwell's equation: + Our third Maxwell's equation: − :$\vec{\nabla}\cdot\vec{D} = \rho$ + :$\vec{\nabla}\cdot\vec{B} = 0$ where: where: − :$\vec{D} = \varepsilon\vec{E} = \varepsilon_0\varepsilon_r\vec{E}$ + :$\vec{B} = \mu \vec{H} = \mu_0\mu_r\vec{H}$ − with: $\varepsilon, \varepsilon_0, \varepsilon_r$ the permittivity of the medium, of the free space and relative permittivity, respectively. + with: $\mu, \mu_0, \mu_r \,$ the (magnetic) permeability of the medium, of the free space and relative permeability, respectively. + The magnetic field is the curl of a magnetic vector potential ($\vec{A} [Volt-seconds \; per \; metre]\,$): − The electric field is the gradient of an electrostatic potential ($V [Volts]\,$): + :$\vec{B}=\vec{\nabla} \times \vec{A}$ − :$\vec{E}=-\vec{\nabla} V$ + Our fourth Maxwell's equation: − Our second Maxwell's equation: + :$\vec{\nabla} \times \vec{H} = \vec{J}$ − :$\vec{\nabla}\times\vec{E} = 0$ + By combining these Maxwell's equations, we obtain: − By combining these Maxwell's equations, we can easily can obtain the Poisson's equation: + :$\vec{\nabla} \times \left ( \frac{1}{\mu} \vec{\nabla} \times \vec{A} \right ) - \vec{J} = 0$ − :$\vec{\nabla} \varepsilon \vec{\nabla} V + \rho_v = 0$ + ::[[Magnetostatics Basic principles | '''''Basic principles extended''''']] + === Poisson's Equation in Magnetostatics === + For 2D domains, we can reduce the Magnetostatic equation to the [[Poisson's Equation]]. If there is no changes in the Z-direction and Z-component of the magnetic field, then   $\frac{\partial}{\partial z} (·)=0$   and   $\vec{A}=A_z \hat z$    and therefore: − ::[[Magnetostatics Basic principles | '''''Basic principles extended''''']] − === Poisson's Equation in Magnetostatics === + ::$\vec{B}=\vec{\nabla} \times A_z \hat z = \frac{\partial}{\partial y} A_z \hat x - \frac{\partial}{\partial x} A_z \hat y$ − The detailed form of the [[Poisson's Equation]] in Magnetostatics is: + ::$\vec{H}=\frac{1}{\mu} \vec{B} = \frac{1}{\mu_x} \frac{\partial}{\partial y} A_z \hat x - \frac{1}{\mu_y} \frac{\partial}{\partial x} A_z \hat y$ − ::$\frac{\partial}{\partial x}\cdot \left( \varepsilon_{x} \cdot \frac{\partial V(x,y,z)}{\partial x}\right) + \frac{\partial}{\partial y}\cdot \left(\varepsilon_{y} \cdot \frac{\partial V(x,y,z)}{\partial y} \right) + ::[itex]-\frac{\partial}{\partial x}\cdot \left( \frac{1}{\mu_y} \frac{\partial A_z(x,y)}{\partial x}\right) − + \frac{\partial}{\partial z}\cdot \left(\varepsilon_{z} \cdot \frac{\partial V(x,y,z)}{\partial z} \right) + \rho_v(x,y,z)=0$ + - \frac{\partial}{\partial y}\cdot \left( \frac{1}{\mu_x} \frac{\partial A_z(x,y)}{\partial y}\right) - J_z(x,y)=0[/itex] Line 67: Line 68: − For a domain ${\Omega} \,$, we should consider three different boundary conditions: + For a 2D domain ${\Omega} \,$, we should consider three different boundary conditions: * Dirichlet boundary condition: * Dirichlet boundary condition: − ::$\left . V - \bar V = 0 \right |_{\Gamma_{V}}$ + ::$\left . A_z - \bar A_z = 0 \right |_{\Gamma_{A_z}}$ * Neumann boundary condition: * Neumann boundary condition: − ::$\left . \hat n \vec{D} - \bar D_n = 0 \right |_{\Gamma_{q}}$ + ::$\left . \hat n \vec{H} - \bar H_n = 0 \right |_{\Gamma_{q}}$ * Infinit condition (when no physical boundary are presents -free space-): * Infinit condition (when no physical boundary are presents -free space-): − ::$\left . \frac{\partial V}{\partial r} \right |_{\Gamma_{\infty}} \approx - \frac{V}{r}$ + ::$\left . \frac{\partial A_z}{\partial r} \right |_{\Gamma_{\infty}} \approx - \frac{A_z}{r}$ Line 88: Line 89: == References == == References == − # [http://www.answers.com/topic/electrostatics Sci-Tech Encyclopedia: Electrostatics] + # [http://www.answers.com/topic/magnetostatics Reference Answers: Magnetostatics] − # [http://en.wikipedia.org/wiki/Electrostatics wikipedia Electrostatics] + # [http://en.wikipedia.org/wiki/Magnetostatics wikipedia Magnetostatics] − # [http://en.wikipedia.org/wiki/Static_electricity wikipedia Static electricity] + # [http://en.wikipedia.org/wiki/Magnetism wikipedia Static Magnetism] − # [http://en.wikipedia.org/wiki/Electric_charge wikipedia Electric charge] + # [http://en.wikipedia.org/wiki/Electric_currents wikipedia Electric currents] − # [http://en.wikipedia.org/wiki/Electric_force Electric force] + # [http://en.wikipedia.org/wiki/Lorentz_force Magnetic force] − # [http://www.colorado.edu/physics/2000/waves_particles/wavpart2.html Electric force animation] + # [http://en.wikipedia.org/wiki/Magnetic_flux Magnetic flux] − # [http://en.wikipedia.org/wiki/Electric_flux Electric flux] + # [http://en.wikipedia.org/wiki/Magnetic_field Magnetic field] − # [http://en.wikipedia.org/wiki/Electric_displacement_field Electric displacement field] + # [http://en.wikipedia.org/wiki/Poisson%27s_equation Poisson's Equation] # [http://en.wikipedia.org/wiki/Poisson%27s_equation Poisson's Equation] − # [http://electron6.phys.utk.edu/phys594/Tools/e&m/summary/electrostatics/electrostatics.html Electrostatics Summary] == The Finite Element Method for Magnetostatics == == The Finite Element Method for Magnetostatics ==

## General Description

The KRATOS Magnetostatic Application deals with the Finite Element Analysis of problems in magnetostatics. Though the mathematics and general formulation is quite similar to Electrostatics, Magnetostatics presents important differences at a conceptual and a programming level. Therefore, if you are a beginner in electromagnetism or programming electromagnetic applications, we strongly recommend you that you first start with the Electrostatic application.

The following description of the Kratos Magnetostatic Application takes part of:

At a first glance, it could be said that Electrostatics works with static charges whereas Magnetostatics does it with dynamic charges (or static currents). That's partially true and we avoid by now to argue about it. On the opposite, we are going to consider Magnetostatics as a completely new phenomenon instead of thinking in a kind of 'dynamic' electrostatic.

As Electrostatics, Magnetostatics establishes very basic principles of the Maxwell equations, it is an excellent work at academic level, but it is also a powerful conceptual (and eventually the resulting computing tool) to solve important industrial applications (electrical machines such as motors and transformers, circuit components such as coils, permanent magnets, sensors, magnetic field distribution, etc).

## Theory

Magnetostatics refers to the physical phenomena related to the presence of stationary electric currents in the objects (magnetic materials can be considered as those with internal microcurrents). That means that we ignore any electrostatic charge, the electric field and we presume a constant magnetic field with respect to time.

### Basic principles

Our third Maxwell's equation: $\vec{\nabla}\cdot\vec{B} = 0$

where: $\vec{B} = \mu \vec{H} = \mu_0\mu_r\vec{H}$

with: $\mu, \mu_0, \mu_r \,$ the (magnetic) permeability of the medium, of the free space and relative permeability, respectively.

The magnetic field is the curl of a magnetic vector potential ( $\vec{A} [Volt-seconds \; per \; metre]\,$): $\vec{B}=\vec{\nabla} \times \vec{A}$

Our fourth Maxwell's equation: $\vec{\nabla} \times \vec{H} = \vec{J}$

By combining these Maxwell's equations, we obtain: $\vec{\nabla} \times \left ( \frac{1}{\mu} \vec{\nabla} \times \vec{A} \right ) - \vec{J} = 0$
Basic principles extended

### Poisson's Equation in Magnetostatics

For 2D domains, we can reduce the Magnetostatic equation to the Poisson's Equation. If there is no changes in the Z-direction and Z-component of the magnetic field, then $\frac{\partial}{\partial z} (·)=0$   and $\vec{A}=A_z \hat z$   and therefore: $\vec{B}=\vec{\nabla} \times A_z \hat z = \frac{\partial}{\partial y} A_z \hat x - \frac{\partial}{\partial x} A_z \hat y$ $\vec{H}=\frac{1}{\mu} \vec{B} = \frac{1}{\mu_x} \frac{\partial}{\partial y} A_z \hat x - \frac{1}{\mu_y} \frac{\partial}{\partial x} A_z \hat y$ $-\frac{\partial}{\partial x}\cdot \left( \frac{1}{\mu_y} \frac{\partial A_z(x,y)}{\partial x}\right) - \frac{\partial}{\partial y}\cdot \left( \frac{1}{\mu_x} \frac{\partial A_z(x,y)}{\partial y}\right) - J_z(x,y)=0$

Poisson's Equation extended

### Magnetostatic Boundary Conditions

For a 2D domain ${\Omega} \,$, we should consider three different boundary conditions:

• Dirichlet boundary condition: $\left . A_z - \bar A_z = 0 \right |_{\Gamma_{A_z}}$
• Neumann boundary condition: $\left . \hat n \vec{H} - \bar H_n = 0 \right |_{\Gamma_{q}}$
• Infinit condition (when no physical boundary are presents -free space-): $\left . \frac{\partial A_z}{\partial r} \right |_{\Gamma_{\infty}} \approx - \frac{A_z}{r}$

Boundary Conditions extended