#### Topic: Heat transfer in multilayer concreting

The questions concerns the modeling of heat transfer during layer-by-layer concreting of a structure in Atena.Transport.
I am solving a test problem in demo mode and I want to understand the approach to modeling.

My general logic for solving the problem is as follows:
1. Modeling of all individual volumes of concrete by layers.
2. Creation of dummy and new materials for successively introduced concrete layers on Interval data.
3. Setting Interval data with the options "Material Activity": replacing Dummy and New (real) materials with the release of heat CERHYD.
4. Next, I must introduce the boundary conditions of contact for the outer surfaces of the volumes. Assume that all surfaces are in contact with air with ambient temperature 5 °C. "Moisture Temperature Boundary for Surface" is an appropriate condition for this. These conditions are assigned to all external surfaces of the volumes of new materials at appropriate intervals.

Questions:
a) When solving such a problem, an ArithmeticException arises, associated only with the presence of boundary conditions in the problem. How to fixed this?
b) Replacing dummy materials with new ones is correct, but the temperature of volumes in the new materials is inherited from the dummy material. This makes it impossible to set a fixed initial temperature of the concrete mix that occurs at a new interval.
с) Function"ResetNew" of "Material Activity" for dummy materials relieves internal forces only?

Attach files: http://ge.tt/9WYpft13

#### Re: Heat transfer in multilayer concreting

Dear test,
I. you may be interested in the ATENA Cloud service, see https://www.cervenka.cz/products/atenacloud

II. I suspect the Moisture Temperature Boundary condition may not be properly supported for internal surfaces. Moreover, a temperature+humidity jump at the moment of casting is likely to bring severe numerical issues.

If any of the above 2 gets identified as the main problem source (after eliminating others, see below), you may need to switch to adding the Volumes using the Elements Activity for Volume condition.

III. In any case, similar to eliminating rigid-body motion modes for Static analysis, I suspect a model with this condition at all surfaces is not well-posed. Moreover, I doubt you can prepare a real setup where all surfaces are best represented with this condition, especially the bottom surface.

IV. I strongly recommend to use Layers in GiD to make orientation in your model easier.

V. For the "dummy" material to be later replaced, I recommend to use the simplest model, i.e., modified from the Concrete or Steel template with only the basic options active, i.e., conductivity + capacity.

VI. When meshing your model, I get warnings that nonexitant materials are referred in Show Material Activity - please correct that, keeping in mind that separate materials are need for each Interval. I mean you can only replace the material for all elements with the "old" material assigned.

Regards.

#### Re: Heat transfer in multilayer concreting

Thanks for the support!
I adjusted the model according to your recommendations. Now this model correctly illustrates the appearance of new heating layers of young concrete over old ones. But surprisingly, deleted volumes (not yet existing) have temperature contact with materially existing volumes. That is, in the first interval, heat exchange occurs between the first layer of young concrete and the second dummy layer, which will only be created in the next interval. Why is this happening? How to achieve isolation of the surface of the future contact of the volumes?
The next step in clarifying the conditions of the problem will be the modeling of environmental conditions. But still as a result of creating any "Moisture Temperature Boundary for Surface", an ArithmeticException error appears...
http://ge.tt/9MONSv13
I would be grateful for your help!

#### Re: Heat transfer in multilayer concreting

Dear test,
1. when using the material model for fresh concrete (CerHyd), we urgently recommend to use the ConMix utility to generate the properties. Otherwise, it is extremely easy to end with an inconsistent set of the material parameters. At the Basic tab, please choose "FILE" for Type of definition CERHYD, and enable the checkbox "Run ConMix for CERHYD".

2. You disable the moisture degree of freedom in Interval Data (Fixed moisture Dof), but at the same time, define a BC for this DoF?

3. The step length about 10 hours (4 days in 10 steps) is way too long if you are interested in the temperature development in early age concrete. Usual step lengths in similar cases are minutes or even seconds...

4. To be able to capture the gradients near the surfaces, you need to refine the mesh. You may also be interested in the GiD meshing option "Concentrate elements".

5.  I again recommend to use Layers for sorting the entities in your model.

Regards.

#### Re: Heat transfer in multilayer concreting

I am aware of the capabilities of ConMix and the need for "Concentrate elements". Both of these techniques allow you to refine the results. But now I am solving the test problem and first I want to get a reproduction of physical phenomena and processes, and then use the above methods.
Now I want to ask you quite exact question again. Answer to it will allow me to understand how to conduct a dialogue with the program to obtain an accurate result.

So, the only existing volume in the first interval produces heat exchange with a dummy volume, which is not in a given period of time. The model is not true. What needs to be done in the program so that the upper surface of the existing volume (the adjacent surface of the existing and fictitious volumes) ceases to receive heat from the dummy volume? In addition, I want the existing volume to have a boundary condition on this surface, equivalent to its contact with atmospheric air at a temperature of 5 °C. How can I do this step by step?

In addition, he reducing of the time step really allowed us to avoid the arithmetic error of convergence only in the first interval. But now in the subsequent stages I observe another error "AccessViolationException". How to fix this?

http://ge.tt/4yTfbx13

Thanks!

#### Re: Heat transfer in multilayer concreting

Dear test,
1. as already mentioned, without ConMix, the risk of setting the properties in an inconsistent way is extreme.

2. I still get a message about nonexistent material being replaced through "Show Material Activity" in Int2.

3. As already discussed, having the Moisture Temperature condition at all surfaces is similar to prescribing forces at all surfaces in a Static analysis - the system is ill-posed. Moreover, please explain the real setup - especially, the bottom surface?

4. After you fix the above issues, send us the model again. We will see if/which problems persist...

Regards.

#### Re: Heat transfer in multilayer concreting

Additional note: it seems an error source is that the condition applied on a Surface between existing and not-yet-existing Volume is randomly considered as belonging to one of the 2 volumes. Therefore, I suggest to duplicate the surfaces (such that each Volume has its own one) and connect the Volumes using Master-Slave (Fixed Contact for Surface).

The easiest way to duplicate the surfaces is to move the middle Volume e.g., 2 meters horizontally and then back again, with the Collapse option disabled.

Regards.

#### Re: Heat transfer in multilayer concreting

Dear dpryl,
I thank you very much for your help! Using your advice, I managed to avoid most of the errors in my test task!

In a previous post, you also recommended using ConMix. However, when I use the CERHYD parameters from FILE, they are not transferred to the material because the result is a model with an isothermal process. While the CERHYD parameters sets by USER, the material heats up.
http://ge.tt/77BtGM23

#### Re: Heat transfer in multilayer concreting

Dear test,

1. I see no Conditions defined in ConMixTest.gid? This means that all surfaces are insulated for both heat and humidity, and the problem is similar to a Static model with only force boundary conditions - the equation system is not properly conditioned.

2. If I remember correctly, there has been some work related to the CerHyd model since 5.3.5 (I remember some issue with units...). Although we have not yet prepared a special DEMO installation from version 5.6.1, it is possible to install the current version 5.6.1 and use it without a key in DEMO mode (compared to the special DEMO installation, you need to click the message about switching to DEMO every time). If you are primarily interested in features related to hydration, I recommend to install the current 5.6.1 without a key to try it.

3. I would recommend to define Monitors to follow at least the Temperature and Humidity at a few points in the model. I especially recommend the option Monitor for Point Nearest.

Regards.

#### Re: Heat transfer in multilayer concreting

Dear dpryl!
1. In this test problem, I did not set the boundary conditions. This task was created only for testing the inheritance of material properties from ConMix.
2. The problem with ConMix-GiD-Atena communication is observed in both versions of Atena.
I did not fully understand your hint about the problem with units.

I find the cause of the error in empty lines in the output file at the places where the ConMix data was inserted:
SPECIFIC
/
;

So far, I see 2 options for assigning missing data to a material from ConMix Output:
- manual data entry into the input file (.ccs);
- data transfer to standard windows for setting material properties.
These are temporary solutions that I have come to at the moment, but I would like to pay attention to the problem so that it can find a solution in the future if possible.
Once again, I thank you very much for your advice in the feedback!

#### Re: Heat transfer in multilayer concreting

Dear test,
we have checked ConMix works in the current version.

I. Please note you need to save your model (such that it has a name and working directory) before running ConMix.

II. The working directory can also be a problem if you try to work directly with a model from a network drive (unless you map the remote disk to a letter, and access the model through that letter).

III. If I remember correctly, the generated data are exported when you end ConMix - in other words, GiD can not access them if you keep the ConMix window open and switch back to the GiD window.

IV. .ccs is NOT the Input File (.inp), but just an ATENA Studio Project file. However, I strongly discourage from trying to manually edit these files.

Ad 2.: In older ATENA versions, there were some misinterpretation of the ConMix data (generated in some unit set, then in ATENA interpreted as if in other units) - that is why you need to use the current version if you plan to work (or even just play) with the hydration heat modelling.

Regards.

#### Re: Heat transfer in multilayer concreting

Hi!

Let me continue the dialogue on the topic of working at Atena. Transport.

I am setting the CCTransportMaterial properties for young concrete in a massive structure and want to account for the increase in hydration rate in the heated core.
In Atena_Theory it is written that I must specify additional parameters in the tabs "Temperature" and "Temperature Advanced". However, the meaning of the following parameters is completely unclear to me:
K TEMP TEMP LEVEL7,
C TEMP TEMP LEVEL7
and also
K TEMP H,
K TEMP W,
K TEMP GRAV,
C TEMP H
C TEMP W
C TEMP T.
Unfortunately, I did not find a description of these abbreviations in the manual.
And I have no idea how I can define functions for these parameters in "Temperature Advanced Variables" tab.