setting up body to body radiation

[dharhay]

I am stumbling on the initial setup of body to body radiation on a series of pipes.  I have pipe 1 interacting with pipe 2, but pipe 2 interacts with both pipe 1 and pipe 3 and so on until the end of the series where you repeat with last interacting with the next to last only.  The selecting of surfaces and making an enclosure are the points where I feel that I am failing.  The quote below is from the instructions of body to body radiation, but what is it telling me to do?

"Put the surfaces to be involved in the radiation on a unique surface number, namely, the highest surface number of any of the lines making the elements that radiate. To determine which of the six possible sides of a brick element are involved in the radiation, the solver checks the surface number of each line making an element. Each face that has a majority of these lines (3 of 4 sides, or 2 of 3 sides) on the highest surface number can be involved in the radiation. Faces whose lines are not on the highest surface number on the element cannot be involved in the radiation."

Why are lines mentioned along with surfaces? Am I renaming surfaces? Any help is appreciated.

[AstroJohnPE]

Hi Dave,

These days, that description from the help essentially applies to hand-built models only. If you are working with a CAD model, then you have presumably split the faces if necessary so that  just the region(s) involved in radiation is(are) on a different surface number.

In a nut shell, there are two steps for body-to-body radiation.

1. Define the emissivity for all of the surfaces that will radiate between each other. Let's call these "surfaces" Radiation Surfaces. You can do this on a part/surface basis, or use all of the surfaces from the entire Part. So you will indicate that the outside surface (or surfaces) of pipe 1 are a Radiation Surface, outside surface(s) of part 2, outside surface(s) of part 3, and so on.
2. Tell the software which set of Radiation Surfaces will radiate to each other but to nothing else (except for the surrounding environment). This is called an Enclosure. Since pipe 1 sees pipe 2, and pipe 2 sees pipe 3, pipe 1 and 3 can interact by reflection and re-radiating. So those three pipes go into one Enclosure.

Step 1 is done by clicking the "Define Surfaces" button on the main dialog. Then click "Add surface" for each Radiation Surface you need to create. This button gives a small dialog where you use pull-down lists to choose one part and one (or all) surface, then click OK. Then you define the emissivity for the Radiation Surface just created. Repeat for all of the other Radiation Surfaces.

After creating all of the Radiation Surfaces, you can click the OK button to close the Body-to-Body Radiation Surface dialog to get back to the main dialog. Click the "Add" button in the Surfaces selection frame to add each Radiation Surface to the enclosure. This has to be done one Radiation Surface at a time, but it actually doesn't take too long. As you add one Radiation Surface to the enclosure, it disappears from the list. So you can click "Add" and "Ok", "Add" and "OK", etc. without looking too closely at what you are doing.

Chances are that all of your pipes will be in the same enclosure, but that depends on what you are working on. It sounds as if all of your pipes lie in the same plane. So pipe 1 sees pipe 2 and the environment, but pipe 2 blocks pipe 1 from seeing any other pipe. Pipe 2 radiates to pipes 1 and 3 and the environment. And so on down the line. If this is the case AND each pipe is split into two surfaces with the hemispherical surfaces of adjacent pipes facing each other, you could technically define a different enclosure for each pair of pipes, but that puts a lot of work on you. (If the pipes were split in the other direction so that the two surfaces on pipe 1 can see the two surfaces of pipe 2, then EVERYTHING needs to be in the same enclosure. The same part/surface cannot be involved in more than one enclosure.) It is easier for you to turn on the shadowing (so that pipe 1 cannot "see" pipe 3) and put all of the pipes into one enclosure. However, this puts a lot of the computations on the software, so that analysis will take a lot longer to get started (as it creates the body-to-body network of what element sees what other elements).

Finally, the FEA Editor only has lines. The properties of each lines (Part #, Surface #, and Layer #) that form an element will determine different characteristics of that element. For example, you may have guessed that the surface # is used to apply a load (such as a pressure) to a surface. Now imagine 1 brick element - 12 lines. Imagine that each line is on a different surface number 1 through 12. When you select surface 5 and apply a pressure, which faces receive the pressure? Both faces attached to the line on surface #5? The software was developed over the years that required a majority of the lines on a face be the same surface number before a surface load would be applied. Note that this rule does not apply to plate elements!

Sorry for going on so long.

[dharhay]

Thanks so much John. This makes more sense now. I will get back to this in a few days.

[cid:image001.jpg@01CF020E.A94DF550]



David Harhay, P.E.

Principal Engineer

Fives Bronx, Inc.

8817 Pleasantwood Ave. NW

North Canton, Ohio, 44720 - United States

Tel: 330-244-1960 ext. 264 Fax: 330-244-1961


david.harhay@fivesgroup.com

www.fivesgroup.com


[cid:image002.jpg@01CF020E.A94DF550]

[dharhay]

Happy Holidays John,

I have been following your post on setting up the body to body radiation. In the Step 1 I see that in the dialog box the Surface Number is greyed out and 'All' is the selection.  This rules out using P1S2 with P2S3...P4S2 with P5S3, which is the point of the surfaces and the enclosure.  I am confused.

Also, if you make enclosures by mistake there is no way to eliminate them. At the stage of setting up enclosures, they disappear from the selection so that S1P2 cant be used with P3 because P2S3 was already used with P1.

There is something wrong with the program or the instructions are not complete.  I am not as familiar as you, but there is some functionality missing.

Can you look at your post and possibly add some more description to get me over this part of the setup?  The body to body will significantly add to the validity of the model.  Thanks so much.

[AstroJohnPE]

Hi Dave,

Sorry, but I do not know why the surface numbers would be grayed out when defining a new Radiation Surface. Just to clarify, is the drop-down arrow grayed out so that you cannot get to the list of surfaces, or does the arrow work to show the surfaces but some (or all) of the surface numbers listed are grayed out?

I presume from your description that the parts actually have multiple surfaces. One thing to check is to make sure that all of the information (part number, element definition, material properties) are defined for the part. There maybe some interlock that prevents selecting the surface until the software knows ABC about the model. Is there some other type of load applied to the surfaces or part? In theory, all other loads except for surface radiation should be compatible with body-to-body radiation.

Another suggestion is to have all parts visible and not suppressed before accessing the body-to-body radiation dialog. It does some strange things with "disabling" a radiation surface if the corresponding surface is hidden. (And it may be difficult to undo this automatic disabling!)

What type of elements are you using? What version of the software are you using?

About the enclosures, you are correct that there is no means of deleting an enclosure. The best you can do is remove any radiation surfaces that you want to use in another enclosure, and then disable the enclosure (the checkbox "Enclosure participates in calcaulation" at the bottom of the dialog). Click the drop-down for "Surfaces comprising enclosure", pick the radiation surface you want to remove from the enclosure, and then click the "Remove surface" button in the "Surfaces" frame just to the right. Once a surface is removed from enclosure X, it is available for adding to another enclosure.

I don't see any big errors in my description, but I have tidied it up a little bit here:

In a nut shell, there are two steps for defining body-to-body radiation:

1) Define the emissivity for all of the surfaces that will radiate between each other. You can define the radiation surfaces on a part/surface basis, or use all of the surfaces from the entire Part. So you will indicate that the outside surface (or surfaces) of pipe 1 are a Radiation Surface, outside surface(s) of part 2 are another radiation surface, outside surface(s) of part 3, and so on.

2) Tell the software which set of Radiation Surfaces will radiate to each other but to no other radiation surfaces. (The only other thing  the enclosure can radiate to is the surrounding environment). This set of radiation surfaces is called an Enclosure. Since pipe 1 sees pipe 2, and pipe 2 sees pipe 3, pipes 1 and 3 can interact by reflection and re-radiating. So those three pipes go into one Enclosure.

Because there are 4 different dialogs (maybe more if I miscounted) involved with body-to-body radiation setup, and the titles are similar, I will refer to them as follows:

Dialog A: the main dialog accessed from ("Setup > Body-to-body Radiation"). The official title is "Analysis Parameters - Body-to-Body Radiation".

Dialog B: the define Radiation Surfaces dialog accessed from the "Define surfaces" button on the main dialog. The official title is "Analysis Parameters - Body-to-Body Radiation Surfaces".

Dialog C: the dialog where you choose the part and surface that define one Radiation Surface, accessed from the "Add surface" button on dialog B. The official title is "Analysis Parameters - Part and Surface Selection".

Dialog D: the dialog where you choose which radiation surface is in the enclosure, accessed from the main screen (dialog A) by clicking the "Add surface" button located to the right of the "Surfaces comprising enclosure" drop-down. The official title is "Analysis Parameters - Enclosure: Surface Selection".

Step 1 is done by clicking the "Define surfaces" button on the main dialog (dialog A, command path "Setup > Body-to-body Radiation"). Let's call these "surfaces" that you are defining "Radiation Surfaces" to avoid confusion with the surface numbers shown by the software. That is, other than the order in which you create them, there is no direct correlation between the Radiation Surface number that gets defined on dialog B and the surface numbers shown under each part in the browser.

After getting to the define surface dialog B, click "Add surface" for each Radiation Surface you need to create. This button gives a small dialog C where you use pull-down lists to choose one part and one (or all) surface, then click OK on dialog C. Then you define the emissivity for the Radiation Surface just created. Repeat this step for all of the other Radiation Surfaces required. You do not need to click "OK" on dialog B after defining each radiation surface. I know that I have the tendency to do that. It is okay to define one radiation surface after another since they get automatically "applied" to the model when you define each new surface. If you do click the "OK" on dialog B before you are done defining radiation surfaces, just click the "Define surface" button on dialog A to get back to the dialog B and continue to "Add surface".

After creating all of the Radiation Surfaces, you can click the OK button on dialog B to close the Body-to-Body Radiation Surface dialog to get back to the main dialog A.

Step 2 consists of clicking the "Add surface" button in the Surfaces frame to add each Radiation Surface to the enclosure. This has to be done one Radiation Surface at a time, but it actually doesn't take too long. As you add one Radiation Surface to the enclosure (dialog D), it disappears from the list. So you can click "Add surface" on dialog A, then "Ok" on dialog D, "Add" on dialog A and "OK" on dialog D, etc. without looking too closely at what you are doing if you want to add all of the radiation surfaces to an enclosure. Note that you can press the space bar to "click" on the OK button, so no mouse movement is needed. Use one hand to click the mouse and the other hand to press the space bar!

Step 3 consists of defining other parameters, such as whether shadowing occurs (one radiation surface blocks another radiation surface from radiating directly to a third radiation surface), the value for the ambient temperature, and a few special controls on the "Parameters" tab. See the documentation.

If you are still having problems, you may be able to attach an archive of your model (or even a test model that has no trade secrets). See the post "Create, Post, or Provide an Archive of your model".

[dharhay]

Hello John, I asked for help from the support crew.  There was data not able to be accessed for what ever reason and this did not allow me to go forward.  That is straightened out.  Autodesk did say that coupled heat transfer (radiation, convection, and body to body) are not effectively handled by Simulation.  There were areas of cooling that if there were body to body would not have cooled so much.  The Simulation CFD could handle the coupled heat transfer.

Thanks for your responses.

Dave Harhay