Material properties

1. summary How to create a new material

Table of Contents Introduction Material definition Instantiation `set_density()` `set_capacity()` `set_conduc()` `set_isotherm()` `set_perm_vapor()` `set_perm_liquid()` `set_perm_air()` Calling properties Switch materials

Introduction

As shown on the [Inputs] page, creating the `mesh` object for the simulation requires including a material object in the arguments of the `Mesh` instantiation

This means that the `hamopy\materials\standard.py` file contains the definition of an object called `wood_fibre`, which is of the `Material` class and includes all material data.

Material definition in hamopy is a bit tricky, as it was designed to give the user maximum freedom for defining fully customisable transport properties.

This page tells you how to

  * [#Material_definition define] a new material,
  * [#Calling_properties use its properties] once they have been registered,
  * [#Switch_materials modify] a material in an existing mesh.

Material definition

Instantiation

For purposes of reusability, the definition of a new material should preferably be done in a separate file which you can then import into your script (like `hamopy.materials.standard` above)

Once there, you may start by instantiating a new `Material` object:

The instantiation may take up to three arguments: the material name, its dry density and specific heat. || *Argument name* || *Format* || *Default value* || || `name` || `string` || `new_material` || || `rho` || `float` || 1000 kg/m^3^ || || `cp` || `float` || 1000 J/(kg.K) ||

Once created, the `Material` object contains the following set of methods to register all material properties.

`set_density()`

If not provided at the instantiation, you can specify the dry density of the material like so:

`set_capacity()`

In the current state of hamopy, the heat capacity of the dry material can be defined as a function of the temperature.

When called, the value of the heat capacity will then be `cp = cp_0 + T(°C) * cp_t`

The default value for `cp_t` is 0.

`set_conduc()`

The thermal conductivity may be defined as a function of the moisture content and temperature.

When called, the value of the conductivity will then be `lambda = lambda_0 + w(kg/m3)/1000 * lambda_m + T(°C) * lambda_t`

The default value for `lambda_m` and `lambda_t` is 0.

`set_isotherm()`

There are currently two methods for defining the sorption isotherm:

  * A 3^rd^ degree polynomial interpolation, fitted on a list of measurement points:

where the list given in the `'W'` key are the values of the moisture content measured at the relative humidities `'HR'`.

  * The second method for defining the sorption isotherm is the van Genuchten mono- or multimodal law:

`set_perm_vapor()`

There are currently two methods for defining the water vapor permeability:

  * By interpolation between measurement points:

  * With the Schirmer law:

`set_perm_liquid()`

There are currently two methods for defining the liquid permeability:

  * With an exponential law:

  * With the Durner multi-modal law:

Note that if this method is not used in the definition of a material, this permeability will be set to `0` and liquid transfer will not be considered in the calculation.

`set_perm_air()`

The air permeability should be given in (m^2^). Only a constant value is expected:

Calling this method is optional: the default air permeability is `0`.

Calling properties

Once defined, all properties may be called as fonctions of the temperature `T` and capillary pressure `p_c`. The following methods are bound within the `Material` class for this purpose

|| *Method* || *Returns* || *Required arguments* || *Optional arguments|| || `rho` || Density || || || || `cp` || Heat capacity || || `T` || || `conduc` || Thermal conductivity || || `p_c`, `T` || || `w` || Moisture content || `p_c` || `T` || || `c_w` || Derivative of the moisture content || `p_c` || `T` || || `delta_p` || Vapor permeability || `p_c` || `T` || || `k_l` || Liquid permeability || `p_c` || `T` || || `k_air` || Air permeability || || ||

• Important*: hamopy is written with the capillary pressure as the driving potential for moisture transfer. All variables depending on the humidity are therefore methods expecting `p_c` as input argument, rather than the value of relative humidity or vapor pressure. Some functions are however available in the [Library] to easily switch from one another.

Switch materials

Once a material has been integrated into a `Mesh` object, it is still possible to change some of its properties and tell the mesh of the modifications:

This functionality is particularly interesting when running a large number of simulations with different material properties, like in case of a sensitivity analysis. The instantiation of the `Mesh` and `Material` objects is not repeated, which saves some time.

[Overview]