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Método de Celdas de Boltzmann (LBM)

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El método de celdas de Boltzmann o lattice Boltzmann Model emplea un sistema de ecuaciones basados en la teoría de transporte de Boltzmann para calcular la velocidad de un fluido.

>Model

ID:(1030, 0)



Density

Equation

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If the parameters are calculated by averaging over the speed using

\chi_k(\vec{x},t) =\displaystyle\frac{1}{c(\vec{x},t)}\displaystyle\int d\vec{v} f(\vec{x},\vec{v},t) \chi_k(\vec{x},\vec{v},t)



the mass density estimation is obtained by:

\rho(\vec{x},t) = m\displaystyle\int f(\vec{x},\vec{v},t)d\vec{v}

ID:(8458, 0)



Speed of the Flow

Equation

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If the parameters are calculated by averaging over the speed using

\chi_k(\vec{x},t) =\displaystyle\frac{1}{c(\vec{x},t)}\displaystyle\int d\vec{v} f(\vec{x},\vec{v},t) \chi_k(\vec{x},\vec{v},t)



the velocity of the flow is calculated by integrating the velocity distribution function on all velocities by weighing the velocities:

\vec{u}(\vec{x},t) = \displaystyle\frac{m}{\rho}\int \vec{v}f(\vec{x},\vec{v},t)d\vec{v}

ID:(8459, 0)



Temperature

Equation

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If the parameters are calculated by averaging over the speed using

\chi_k(\vec{x},t) =\displaystyle\frac{1}{c(\vec{x},t)}\displaystyle\int d\vec{v} f(\vec{x},\vec{v},t) \chi_k(\vec{x},\vec{v},t)



and the equipartition theorem is considered, the temperature can be estimated by integrating the kinetic energy weighted by the velocity distribution divided by the gas constant:

T(\vec{x},t) = \displaystyle\frac{m}{3R\rho}\displaystyle\int (\vec{v}\cdot\vec{v})f(\vec{x},\vec{v},t)d\vec{v}

ID:(8460, 0)



Tension tensor

Equation

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If the parameters are calculated by averaging over the speed using

\chi_k(\vec{x},t) =\displaystyle\frac{1}{c(\vec{x},t)}\displaystyle\int d\vec{v} f(\vec{x},\vec{v},t) \chi_k(\vec{x},\vec{v},t)



the flow tensor is calculated by integrating the velocity distribution function on all velocities by weighing the velocity differences:

\sigma_{ij} = m\displaystyle\int (v_i-u_i)(v_j-u_j)f(\vec{x},\vec{v},t)d\vec{v}

ID:(8461, 0)



Discretization function

Equation

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In the case of the discretization in the LBM models we work not with functions of the speed if not with discrete components. In this way the i component is defined by:

f_i(\vec{x},t)=w_if(\vec{x},\vec{v}_i,t)

where w_i is the relative weight.

ID:(8466, 0)



Densidad del Gas

Equation

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la densidad en un punto \vex{x} y tiempo se calcula simplemente sumando todas las distribuciones de particulas f_i en dicho punto y tiempo:

ID:(8492, 0)



Densidad de momento del gas

Equation

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Con la descritización

f_i(\vec{x},t)=w_if(\vec{x},\vec{v}_i,t)



la ecuación

\vec{u}(\vec{x},t) = \displaystyle\frac{m}{\rho}\int \vec{v}f(\vec{x},\vec{v},t)d\vec{v}



pasa a ser

\rho(\vec{x},t)\vec{u}(\vec{x},t)=m\sum_i\vec{e}_if_i(\vec{x},t)

ID:(8493, 0)



Temperatura del Gas

Equation

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la densidad en un punto \vec{x} y tiempo se calcula simplemente sumando todas las distribuciones de particulas f_i en dicho punto y tiempo:

T(\vec{x},t)=\displaystyle\frac{m}{3R\rho}\sum_i(\vec{e}_i\cdot\vec{e}_i)f_i(\vec{x},t)

ID:(8897, 0)



Boltzmann equation

Equation

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The Boltzmann function describes the transport of a particle system described by the velocity distribution function:

\displaystyle\frac{\partial f}{\partial t}+v_i\displaystyle\frac{\partial f}{\partial x_i}=C(f)

Where the term C describes the interaction (collisions) between them.

ID:(8462, 0)



Teoría de Grad de los 13 momentos

Equation

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La distribución de velocidades se puede representar como un polinomio ortogoan de Hermite

f^N(\vec{x},\vec{v},t)=\omega(\vec{v})\displaystyle\sum_{n=0}^N\displaystyle\frac{1}{n!}a^{(n)}(\vec{x},t)\mathcal{H}(\vec{v})

ID:(8463, 0)



Coeficiente de Orden 0

Equation

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El coeficiente de orden cero es

a^{(0)}=\displaystyle\int f(\vec{x},\vec{v},t)d\vec{v}=\rho

ID:(8464, 0)



Coeficiente de Orden 1

Equation

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El coeficiente de orden cero es

a^{(1)}=\displaystyle\int \vec{v}f(\vec{x},\vec{v},t)d\vec{v}=\rho\vec{u}

ID:(8465, 0)



Coeficientes

Equation

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Los coeficientes son:

a^{(n)}(\vec{x},\vec{v},t)=\displaystyle\int f(\vec{x},\vec{v},t)\mathcal{H}^{(n)}(\vec{v})d\vec{v}=\displaystyle\sum_if_i(\vec{x},t)\mathcal{H}^{(n)}(\vec{v})

ID:(8467, 0)