A few questions on hydraulic fracturing using DFNFlowEngine

Hi,

I have a few questions on modeling hydraulic fractures using DFNFlowEngine. My model size is 40m by 40m by 40m and I have precrack (in shape of a circle) on the x-y plane located exactly at the center of the model. The center of the circle of the precrack is located at 20,20,20. Here are my questions:

1. I want to pump in 10m^3 of liquid in my precrack @ 1m^3 per second. To do this, this is what I have done:
ti = O.time
def Pumping():
if O.time<(ti+10):
flow.imposeFlux(Vector3(20,20,20),-1)
print("PUMPING")
else:
flow.imposeFlux(Vector3(20,20,20),0)
print("PUMPING STOPED")
O.engines=O.engines+[PyRunner(iterPeriod=1,command='Pumping()')]

I am concerned about how I switch off the pumping. is it correct? Should I use clearImposedFlux?

2. I want to keep the fluid inside the precrack (or the newly developed crack). This means that there is no leakoff. To do this, I did this:
flow.permeabilityFactor=0
Is this correct? Will this keep the fluid only in the crack?

3. Going back to question 1, when I pump in fluid at 20,20,20 (the center of the precrack), I would expect that the crack would grow radially (i.e. begcome a bigger circle in the xy plane). However, the bonds (between the particles) just above and below (20,20,20) start to break first and crack mini cracks in the z direction before the precrack starts to grow radially. How can I prevent the crack from propagating in the z direction? I am aware that my imposed flux is a singular point and therefore, this is bound to happen. Should I change the way I load the flux?

4. What is flow.jointsResidualAperture ? According to the YADE manual, it is "residual aperture of joints". Is this the width of the precrack? Is so, how does this value effect the calculations?

5. What is flow.clampKValues? What is K? I read the manual, but I still don't understand what this does.

6. Should I use flow.blockHook for all the pores that are not within the precrack to increase the computations?

Thank you so much for your help. I really appreciate everyone's time in responding to these questions

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 Revision history for this message Najm (mrhappy) said on 2020-07-14: #1

I have some follow up questions:
7. How does one decide on the critical time step that is required when simulating a model with DFNFlowEngine?

8. According to [1] equation 23, the local inter-pore conductivity is a function of alpha and beta values. Is flow.apertureFactor beta and flow.permeabilityFactor alpha? If not, how do I define alpha and beta values?

Again, thank you so much!

[1] Intensity and volumetric characterizations of hydraulically driven fractures by hydro-mechanical simulations (https://www.sciencedirect.com/science/article/pii/S136516091730076X?casa_token=9bufyK82gXEAAAAA:gbytchivM6TtYR6wwPPLvijU4YfGx91hFM1hBMRyChdb40QmYAn8Zxei15dVzMs9qMfrRIuv9Q )

 Revision history for this message Launchpad Janitor (janitor) said on 2020-07-26: #2

This question was expired because it remained in the 'Open' state without activity for the last 15 days.

 Revision history for this message Robert Caulk (rcaulk) said on 2020-07-27: #3