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Define Thermal Properties

The Define Thermal Properties define_thermal_prop option, located in the toolbar or by selecting Properties > Define Material Properties, is used to specify the thermal parameters for each material. Define Thermal Properties is ONLY applicable if you are enabling Thermal Analysis from the Project Settings menu.

The options available in the Define Thermal Properties dialog correspond to the selected Thermal Method specified in the Project Settings dialog:

  • If the Thermal Method = Static Temperature, then the thermal characteristics are not provided.
  • If the Thermal Method = Finite Element Analysis, then you will be able to define the thermal characteristics of each material.

The available options are described below.

Type

When there is Static Temperature included in thermal analysis, the Static Temperature Mode can be chosen from defining a Constant or using a Grid (The Grid is a user defined Temperature Grid from the Thermal menu).

Water Content may be specified when FEA is included in the thermal analysis (either steady or transient). It can be simply defined by a Water Content Value, or the water content value Use from Groundwater that calculated from the chosen groundwater model.

Thermal Conductivity

This option is available when thermal method is steady or transient thermal FEA. In RS2, six methods are provided to define the Thermal Conductivity of a material. For each method, the parameter values for common materials are listed by clicking the Parameter Values Button button. The methods with their required inputs are described below.

  1. Constant
  2. The unfrozen conductivity, frozen conductivity, and frozen temperature of the material should be defined.
  3. Johansen
  4. The equations are differ depending on the soil type (i.e., fine, coarse, crushed rocks, or peat). The quartz content should be inputted. For peat soil, the dry conductivity, saturated unfrozen conductivity, and saturated frozen conductivity are required additionally.
  5. Johansen-Lu
  6. The Johansen-Lu approach is improved based on the Johansen approach. The soil type (fine or coarse) with its quartz content is required.
  7. DeVries
  8. The De Vries approach uses thermal conductivity fractions of their constituents for estimation. The particle conductivity is required.
  9. Cote and Konrad
  10. The Cote and Konrad method involves the relationship between the normalized thermal conductivity and degree of saturation for thermal conductivity estimation. Required inputs including the particle conductivity, unfrozen and frozen kappa (κ that accounts for soil type), chi (χ that accounts for soil type), and eta (η, an empirical constant).
  11. Custom
  12. The thermal conductivity can be customized as either temperature or water content dependent values. User defined data can be inputted in a table of temperature / water content vs. thermal conductivity.

Thermal Heat Capacity

The Thermal Heat Capacity is available for Transient Thermal FEA only. The thermal volumetric heat capacity for soils can be determined by three ways in RS2: constant, Jame Newman, and custom. Other than soils, the typical specific heat capacities for common materials are listed in the RS2 Thermal Analysis Theory Manual.

  1. Constant
  2. Required inputs are the unfrozen volumetric heat capacity, frozen volumetric heat capacity, and frozen temperature.
  3. Jame Newman
  4. When the Jame Newman method is selected, the soil specific heat capacity should be inputted to estimate the volumetric heat capacity.
  5. Custom
  6. The thermal volumetric heat capacity can be customized as either temperature or water content dependent values. User defined data can be inputted in a table of temperature / water content vs. thermal volumetric heat capacity.

It is optional to Include Latent Heat for thermal heat capacity calculation in transient thermal FEA. When the latent heat is considered, the energy absorbed or released during phase change is accounted for. Latent water is given as Lw = 3.34E + 05 kJ/ton in RS2. See the RS2 Thermal Analysis Theory Manual for more detail.

Thermal Soil Unfrozen Water Content

The Thermal Soil Unfrozen Water Content option is available for steady or transient thermal FEA method. The unfrozen water content for soils is critical during soil phase change, and it often displayed using the soil freezing characteristic curve (SFCC). It may also have an impact on heat conductivity and heat capacity.

To be mentioned, the Thermal Soil Unfrozen Water Content option is NOT available under the two conditions:

  • For steady thermal FEA, the Heat Conductivity method is Constant.
  • For transient thermal FEA, the Heat Conductivity method is Constant, and the Heat Capacity Method is Constant with the Latent Heat option OFF.

In RS2, the soil unfrozen water content can be determined by five different methods, as listed below with required input parameters.

  1. Konrad
  2. The Konrad method estimates volumetric unfrozen water content for soils from SFCC of its exponential relationship. Required inputs includes the residual water content, frozen temperature (i.e. the liquidus temperature), and solidus temperature (i.e. the temperature at the end of ice phase change).
  3. Tice and Anderson
  4. The Tice and Anderson method uses a power curve relationship between negative temperature and gravimetric unfrozen water content of soils for estimation. The Input A, Input B, and Frozen Temperature are required to be inputted, where Input A and Input B are the characteristic parameters α and β accounts for the phase composition of frozen soils based on the specific surface area of the soil mineral grains. Typical α and β values for common soils can be found in the RS2 Thermal Analysis Theory Manual.
  5. Soil Water Content in Hydraulics Properties
  6. For this method, a Hydraulic Model can be defined with its associated hydraulic parameters, to calculate the soil water content. A Frozen Temperature is required to calculate suction (ψ). The soil unfrozen water content can then be obtained.

    The available Hydraulic Models are the same as the permeability models provided for hydraulic seepage analysis in RS2, including simple, Fredlund and Xing, Van Genuchten, Brooks and Corey, and Gardner.
  7. Custom
  8. The thermal soil unfrozen water content can be customized as the temperature dependent value. User defined data can be inputted in a table of temperature vs. thermal soil unfrozen water content.
  9. Simple
  10. Assume a stage right before the soil freezing point (Tf) at temperature T0 , and a stage right after the soil freezing point at temperature T1. For the Simple method, it assumes that the phase change happens immediately within the region T0 < Tf < T1. When temperature is below T0, the soil unfrozen water content is zero; when temperature is above T1, the soil unfrozen water content is equal to the soil water content. A SFCC is not used in this method.

Thermal Expansion

The Thermal Expansion option is available for any thermal analysis method. It is optional for the user to consider the Thermal Expansion as a factor in a RS2 thermal analysis. Users can include it by selecting the checkbox to enable the feature and input an Expansion Coefficient (1/length).

Dispersivity

The thermal Dispersivity is available for steady or transient thermal FEA method. It is optional for the user to consider the Dispersivity as a factor in a RS2 thermal analysis. Users can include it by selecting the checkbox to enable the feature and input the Longitudinal Dispersivity and Transverse Dispersivity parameters both in units of length.

For theory and equations about each thermal property listed above, please see the RS2 Thermal Analysis Theory Manual.


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