using feht

Using FEHT

Keith A. Woodbury

Introduction

• FEHT– Is a simple finite element conduction heat

transfer analysis program– Use of this program entails the same basic

steps necessary to solve heat transfer problems with commercial software

– Is restricted to 2-D problems with less than 1000 nodes

– Can solve steady or unsteady (transient) problems

Overview

• Numerical heat transfer analysis requires the following steps– Define geometry– Define mesh for computation– Assign properties– Define boundary conditions (and initial

conditions, if necessary)– Solve for the temperatures– Perform any desired post-processing

Overview (cont)

• We’ll illustrate use of the program via an example -

Open FEHT

Define Geometry

• First set the grid to something convenient for drawing your 2-D geometry

Define Geometry

• Then draw the outline of your object

Define Geometry

• “Draw -> Outline…” tips– The crosshair cursor does not snap to the grid– Holding the “shift” key while drawing

constrains the motion to straight lines– To make a corner you can click and continue

to the next point

Define Mesh• When an outline is complete, the outline

blinks, and the “Draw->Element Lines…” option is activated

Define Mesh

• “Draw->Element Lines…” tips– Elements must be triangular– Element lines can only connect at nodes (you

can’t join an element line to the middle of another element line!)

Define Mesh

• Keep going…

Define Mesh

• It can be tedious with a lot of nodes

Specify Properties• Click on one of the elements (NOT and edge or

node) – the entire outline will begin blinking• Now go to “Specify->Material Properties” on the

menu (or right click on the object)

Specify Properties

• You can choose from a library of materials or select “not specified” and enter your own data

Apply Boundary Conditions

• Either– Use the pointer to drag a box around a region

of the boundary, or– Click on a segment of the boundary

Apply Boundary Conditions

• The selected portion(s) of the boundary will blink

• Choose “Specify->Boundary Conditions” or right click

Specify Boundary Conditions

• Fill in the boundary condition information

Apply Boundary Conditions

• At any time, “Run->Check” will tell the status of your model

• After all boundaries have been assigned conditions, “Run->Calculate”

Solve for Temperatures

Post-Processing

• “View->Temperatures” shows the computed nodal temperatures

• “View->Temperature Contours” makes a color map of the solution

• “View->Temperature Gradients” visualizes the heat flow directions

• “View->Tabular Output” gives a table of the solution that can be cut/pasted