Finite Element Processing > Getting Finite Element Solution > Processing of heat conduction and seepage analysis

 

Processing of heat conduction and seepage analysis

P rocessing of heat conduction analysis is basically the same as that of structural analysis. But a seepage analysis should go through iterative processes of determining the phreatic flow surface which is not necessary in a structural or a heat conduction analysis.

> Setting analysis options for heat conduction analysis

A steady state analysis of a heat conduction problem requires only one cycle of equation assembly and solution process which is identical to the processing of a linear static analysis of a structural problem. This type of processing is described a l ready in "Processing of structural analysis" section of this chapter, and is not repeated here.

> Setting analysis options for seepage analysis

Although both the seepage analysis and the heat conduction analysis are based on the same governing equations, the processing of seepage analysis is different from that of the latter because it requires an iterative procedure determining the phreatic flow surface.

The editable text items of the dialog requires inputting the following values:

   

Datum (Coordinate of zero height) : datum elevation. The hydraulic head is set to 0 at this level.
   

< Datum level>
   

Unit weight of fluid : The unit weight of fluid is used in converting the head to fluid pressure.
   

  Number of time steps : the number of time steps involved in the transient analysis. This value is ignored in a steady state analysis.
   

  Time step size : the length of time between two consecutive steps. This value is ignored in a steady state analysis.
   

Number of iteration within a step : The phreatic surface is determined by iterative computation. This value specifies the maximum number of iterations determining phreatic surface in a steady state analysis. This value is also applied to a transient analysis as the number of iterations within each time step.
   

  Error tolerance for convergence : Another criterion for finishing the iterative p rocess is base on the maximum diff e rence of phreatic surface elevations between the current and the last iterations. One of this and the above criteria is met, the iterative processing is terminated.
   

  Open head increment : The limit of increment in modifying the open head in a iteration cycle.
   

Criterion for open head modification : The open head is incremented on the basis of this criterion.
   

- "By elevation": If this option is on, the node with lowest elevation is searched along the open head boundary, and the phreatic head is set to the head of node. If more than one node has the lowest elevation, only the node with the maximum pressure will be used to set the head
   

- "By pressure": If this option is on, he node with maximum positive pressure is searched along the open head boundary, and the phreatic head is set to the head of node.