How I do a FE steady state thermal structural analysis using Ansys and suggestions.

There are a lot of ways of doing an analysis like this,I am only showing the way I do it.

This is a reliable way, it is probably “old”, but the mostefficient at least for me.

Each person is different, so you can find a better way ofdoing these analysis, I am just giving you an example.

I will not go through every command, but the most “used” ones.

FE= finite element

Steady state= in our case is the state after all the transient effects.Loads do not vary over time.

Thermal-structural- displacements due to thermal effect-stresses due to thermal effect

Examples: mirror that sees beam stop that sees beam

Displacements, slope

Stresses

As you open Ansys

After that

Log file (text file)

To import a model from SD

Command: File-import SAT (mm) {forget iges}Suggestions: in SD

1) position the model with 0,0,0 xyz axis on a corner and with direction of a “main” face to one of the xyz axis.

2) make sure all the features you need for your analysis are on this model (ex. Imprint faces where you need to apply the load).

3) Clean up and use eventual symmetries to simplify the model

See example : copper.pkg –copper.sat.The model will be transferred in wire frame, to see the normal frame do:Plotctrl-style-solid model facets-normal faceting

To create a model from scratch : see later

Change jobname

preferences

Preprocessor (1st part)

Element (see element classification)Real constants (only when needed) Ex.thickness in a shell element.

Material prop.

ANSYS FORTUNATELY doesn’t have “units”, you give your own units depending on the ones you are working in. You have control of what you are doing, so if you mistake them, it is not the fault of Ansys.

The command “select units” just give you the option to be able to read in which units you are working /STATUS, but it DOESN’T INFLUENCE the data

How to input mat. properties:1)You can create a library: Pro-consPro: you have it there, it saves you some time if youreally need to save it ( ex. A lot of temperaturedependent properties). Cons: you can mistake units even if Ansys filter…. Youkind of loose feeling of material properties.

2)You can input your properties each time: Pro-consPro: less chance in making mistakes, you will sooner orlater learn the properties of the material you are dealingwith.Cons: see pro for other method.

Create the model in Ansys.

Ansys is not a CAD program, so it doesn’t have all the nice features of SD. You have to choose if you want to do a model in Ansys or if you want to import from SD based on your geometry and on future parameters.

Suggestions:1)If the model is simple enough to be made in Ansys, I would just go ahead and do it in Ansys.why?

-Sometimes if you import it from SD due to differences in accuracy from SD and Ansys, there can be difficulties in the translation process.Ex: you have more lines or areas than you expect (This can be acceptable, but if you have lines too close in a big geometry it could make more difficult the meshing process)

-You can sometimes have non mating surfaces (but only in complicated surfaces).

-Sometimes the model in Ansys it is easier to mesh, you can probably map mesh it in a direction.

-you can create parameters and change parameters using the text file

-you have more control on your model.

SUGGESTIONS:

when you create the model in Ansys

1) think what is the best way to create your part, and all the features you need to have.This is probably the most “time consuming” part of the problem but if you do it right now, you will not get depressed later.

Remember that Ansys doesn’t have a real UNDO, meaning you can still fix stuff but not always, and if you can sometimes it can be painful. For this reason, save your database often.

Ex: you create the 2D model, you mesh it by extruding it, than you realize that you made a mistake in the 2D, you cannot UNDO the sweeping command, but you probably have to start doing a series of commands, clear volumes, delete volumes only, delete areas ( besides the one that you need), and so on.

You could also control this through your .log file but you will have to rerun your analysis.

2) You can build all in xyz coord, you can use workplanes, there are boolean operations and so on.

3) Picking is still really bad. It is difficult to pick an areasometimes, I will show you a trick.

4) You can anyway select by location and by other parametersand this simplifies a little bit your life.

5) If you have a very complicated geometry you can create components (made of nodes, areas, lines) and assemblies (with multiple components). When you select, you can select based on the name of the component or assy.

Meshing

If your model is a 3D volume generated for ex. in SD, you can use 3D elements, like the Tet 10 nodes elements, with free mesh. Tet 10 work. The mesher now has improved a lot.

If you generate the model, and you can do map mesh, you can use The 2D element (ex. quadrilateral el) and the correspondent 3D (brick el.).

You can control the mesh.-refine, control size of elements

After meshing a model I would suggest doing the following commands-Clear areas-Nummrg,all (remember to check tolerance)This cleans your model from overlapping lines, nodes and areas that can cause error in the solution.

Check mesh:1-You can plot the elements with warning or errors. With the default settings I think Ansys doesn’t allow you to proceed if you have errors in a mesh.You will still be able to proceed if you have elements that are not the best (aspect ratio out of the range of default setting and so on)and you will receive a warning. It is your call at this point to accept the mesh or re mesh the model depending on these warnings and especially on the location of these “warning” elements. This is an ex. of a mesh with no

warnings and no errors

Solution (2nd part)

Before talking in general about thermal loads and structural loads, what they are and how to apply them in Ansys, I will talk a little bit about the thermal load due to the x-ray beam impact on a generic optical component.

Beta: grazing angle (if you consider a crystal you will be interested in the Bragg angle)

The x-ray beam can be approximated with a gaussian function in the two directions. Most of the times this function is pretty flat in one direction so that we can consider it constant. This simplifies our model.

The parameters that define the gaussian function are:

-peak power density Ppd (W/mm2)

-Sigma (mm) related to the FWHM (full width at half maximum) by the following formula: FWHM=2.35 x sigma.

0

0.002

0.004

0.006

0.008

0.01

0.012

-400 -200 0 200 400

GAUSSIAN FUNCTION

Ex:Gaussian function PPd=.01W/mm2

Sigma=173mmFWHM=407mm

F(x)=PPd * EXP(-(x2)/2*sigma2)

How do we calculate the heat from the beam?

-If you are dealing with Undulator or Wiggler ask Steve Marks

-If you are dealing with bend magnet or superbend you have 3 options :

1) Malcolm Howells spreadsheet ( I have a copy and I know

how to use it).

Andrew Franck 2 websites:

http://xraysweb.lbl.gov/webcalc/PowerCalc/flat_mirror.htm

http://xraysweb.lbl.gov/afranck/power_calculations/filter_mirror.htm

3) Howard Padmore Matlab calculator.

Kurtis Carter checked them and found out that the results obtainedfrom these three methods are very similar.

Please consider also the CXRO website for the absorption values of

the materials