SebSta: hat „FAQ General:DefaultMoistureStorageFunction“ nach „FAQ:General:DefaultMoistureStorageFunction“ verschoben

2013-06-13T12:25:49Z

hat „FAQ General:DefaultMoistureStorageFunction“ nach „FAQ:General:DefaultMoistureStorageFunction“ verschoben

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2008-10-02T08:04:40Z

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= (5): Default Moisture Storage Function =

When I do not define a moisture storage function for a material, WUFI uses
a default moisture storage function instead. What does this function look like?


WUFI needs a well-defined moisture field for each time step, so it must assign a
moisture content even to materials which nominally don't have any appreciable
moisture content (e.g. water-repellent mineral wool, air layers etc.).


The default [[Details:MoistureStorageFunction | moisture storage function]] used
by WUFI is described by the function 

<TABLE>
<TR><TD COLSPAN="3"><TT>w = a / (b - phi) + c</TT></TD></TR>
<TR><TD><TT>w</TT></TD><TD ALIGN="RIGHT">[kg/m³]:</TD><TD>water content </TD></TR>
<TR><TD><TT>phi</TT></TD><TD ALIGN="RIGHT">[-]:</TD><TD>relative humidity</TD></TR>
</TABLE>


Since <TT>phi</TT> must be 0 for <TT>w=0</TT>, it follows immediately that 
 <TT>c = -a/b</TT> 
  
The constants <TT>a</TT> and <TT>b</TT> are determined as follows: 
  
<TT>b</TT> is set to 1.0105. 
  
The moisture content at free saturation, wf, corresponds to
a relative humidity of 1 (=100%). Since WUFI also needs a unique relationship
between moisture content and RH for moisture contents above free saturation, this
oversaturation region is assigned RHs greater than 1, up to
<TT>phimax = 1.01</TT>. This value
<TT>phimax</TT> is
reached when the moisture content reaches maximum saturation
<TT>wmax</TT> which is
determined by the [[Details:BasicMaterialData | porosity]]: 
  
 <TT>wmax = porosity * 1000 kg/m³</TT> 
  
Therefore we have 
  
 <TT>wmax = a / (b-phimax) - a/b.</TT> 
  
Solving for <TT>a</TT> yields: 
  
 <TT>a = wmax * b * (b - phimax) /
phimax</TT>, 
  
and thus: 
  
 <TT>w / wmax = phi / (b - phi) * (b - phimax)
/ phimax</TT>. 
  
  
In particular, for <TT>phi=1</TT> we have 
  
 <TT>wf / wmax = 1 / (b - 1) *
(b - phimax) / phimax = 0.047</TT>. 
  
So this pseudo material has a free saturation of <TT>wf = 0.047 wmax</TT>.


[[Bild:e_defaultfspfkt.gif]]

FAQ:General:DefaultMoistureStorageFunction - Versionsgeschichte

SebSta: hat „FAQ General:DefaultMoistureStorageFunction“ nach „FAQ:General:DefaultMoistureStorageFunction“ verschoben

Len: Die Seite wurde neu angelegt: = (5): Default Moisture Storage Function = When I do not define a moisture storage function for a material, WUFI uses a default moisture storage function instead. W...