PVDesign

[xuefengshi]

When I use PVDesign to make Drum, how to set up the diffrent temperature in interal/out surface. thansk

[AstroJohnPE]

Hi xuefengshi,

I assume that you are performing a stress analysis. If not, please let us know what type of analysis you are performing.

• If you made the model using plate elements, you can only specify a "delta Temperature/thickness" in the Element Definition. I suggest that you look at the wiki Help (search for "Delta T") for the precise definition of this input. Then you can specify the average temperature by applying a temperature load. Be sure to include the coefficient of expansion and the thermal load case multiplier (under the "Setup > Model Setup > Parameters > Multiplier" tab).
• If you made the model using brick elements, you will want to perform a heat transfer analysis first so that you have the temperature at every node through the thickness.
• If you are doing something else, then please provide a lot more detail of what that something else is.

[xuefengshi]

I would like to do some stable/transit thermal stress for drum and header of HRSG(see attachment). I try to use PVDesign to generate mesh and like to set up different temperature/pressure on the shell sides. It seems I could only give one temperature/pressure for both sides.

[AstroJohnPE]

Hi xuefengshi

By stable/transit, I believe you are talking about steady state conditions and transient (time varying) conditions. But are the temperatures changing with time, or are other mechanical loads changing with time? If the temperatures are changing, you need to perform a heat transfer (Thermal) analysis first, then use those temperature results in the stress analysis.

By definition, plate elements are "very thin". So usually there is no significant temperature difference between the inside and outside. BUT, you can enter the information in the Element Definition. Note that the input under the element definition applies to the entire part, so you may need to split the model into more parts if the temperatures change over the length. If the inside temperature is Tinside, the outside temperature is Toutside, and the thickness is t, then

•      temperature to apply to model = mean temperature which causes expansion = (Tinside+Toutside)/2. This is enter through any combination of "Setup > Loads > Temperature", "Setup > Model Setup > Parameters > Thermal/Electrical > Default nodal temperature", and "Element Definition > Stress free reference temperature".
•      temperature difference through the thickness = (Ttop - Tbottom)/t. This is entered in the Element Definition. The element normal coordinate (X, Y, Z) controls which side of the plate is top and which is bottom, so you need to use this to determine whether the "inside" or "outside" is "top" or "bottom".

Since a plate element is thin, you only need to apply one pressure to the plate equal to (inside pressure) - (outside pressure). (Even though the surface area is difference on the inside and outside, you can easily take this into account when calculating the one pressure to apply to plates.)

P.S. The commands I gave above are for version 2013 and may be different than version 2014. Also, one of those versions (please check the Release notes in the documentation) was improved to allow multiple pressures to be applied, so you hypothetically can add one internal pressure and one outside pressure.

[xuefengshi]

Thanks John, is there any examples for this aspect. Thanks