Surface/component boundaries do not align with the grid

[amymaxim]

Hi, I am a student trying to model a microclimatic envelope which includes many opening for natural ventilation. I import the openings to microflow and then when I try to run the simultation it appears this message:

Surface/component boundaries do not align with the grid. You may need to re-generate the grid.

Someone could help me to fix this problem?

[vajindarladdad]

Hi,
If you are using older version of IES<VE> then I would strongly recommend you to upgrade IES<VE> to latest version & give a try simulation ?

This error message normally happens if you are modelling a number of zones on different floors and there are partitions overlaping (especially at right angles to each other.)

You can use the "destroy multi-zone space partitions" tool to remove the incorrectly setup partitions.

I hope this has been of some help , if the problem still persists please don't hesitate to contact us here.

[amymaxim]

Hi,

We are using the version 6.1.0.1. The problem is that our model is really big with alot of windows and angled rooflights, so if we try to make the CFD of all the model we have around 30 million cells. Then we decided to divide the model in Model IT in the part of surface and creating the cuts without partitions. Therefore, when we are in CFD the button of "destroy multi-zone space partitions" is not active/highlighted.

Furthermore, we see that after the divisions we can have parts of the room that could have 3.1 million cells but it appears an error about the memory space. The computer is an Intel(R) Core(TM)2 Duo CPU, so shouldn´t the software allow us to have a limit of 6 to 7 million cells?

Thank you for your prompt answer and we are looking forward to hearing from you soon

P.S. Is there any possibility to send the model to IES-VE so they can evaluate the problem if it persists?

[liamh]

It sounds like your ceiling/roof surface is not horizontal. The Microflo mesher doesn't always handle openings that aren't aligned with the Cartesian mesh well .

I would recommend modelling the sloping roof in a series of horizontal steps so any rooflight is aligned with the Cartesian mesh. This will reduce the aspect ratio of your cells and will probably fix the error message you are receiving.

You will only be able to get to the 6-7 million cells if you have enough RAM available for Microflo. You should aim to have 2GB of RAM free for Microflo so you need more than that in your machine to get to 6-7 million cells.

[amymaxim]

Hi liamh, first of all thank you for your answer. However, this is a bad news for us because we cannot model it with intervals of horizontal roof due to the fact that is a hipped roof and it will be extremely complicated to do it.

There is no other solution for this problem, like do some hemisferical grid or something like that for the roof?

Last question, could you tell me how can I assign in my computer that it gives 2GB of RAM for the Microflo? Because when I put to run the simulation it appears green "ticks" in tha part of memory, so shouldn´t that be enough?

Thank you in advance.

[liamh]

There is no other solution for this problem, like do some hemisferical grid or something like that for the roof?

I'm afraid Microflo is Cartesian only, i.e. it uses hexahedral cells with each face orthogonal to each other, with the cell surface normals aligned with the x-, y- or z-directions. This means that if you produce a geometry with a surface that isn't aligned with the Cartesian directions then Microflo stairsteps across that surface anyway. Therefore it can help to stairstep the geometry yourself to control this process. It is really only necessary for surfaces with flow boundaries in them though as Microflo doesn't handle them well - either the boundary placement or the meshing of it.

Last question, could you tell me how can I assign in my computer that it gives 2GB of RAM for the Microflo? Because when I put to run the simulation it appears green "ticks" in tha part of memory, so shouldn´t that be enough?

You should ignore the green tick marks for the memory check. It is very unsophisticated and doesn't know about the 2GB application limit imposed on 32bit MS-windows applications, or other programs you are running. I would recommend that you try and run it on a machine with 3GB of RAM if you wish to get to the 6-7 million cell limit. If it doesn't work then it may be Microflo has an issue with your system. It seems that the memory limit is processor dependent. Your should be OK with a core 2 duo though as it normally happens on quad core systems.