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blast simulation, blast wave, pressure wave simulation

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Old   March 22, 2015, 05:59
Post blast simulation, blast wave, pressure wave simulation
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dewangga yudistira
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hello

I'm trying to make blast simulation, in this case deflaragation / pressure wave blast of hidrocarbon (I used C1 as the fluid)

the simulation will be used transient function, is it better use cfx or the transient?

for the inlet boundary i will use sphere with pressure based on some function, can I input the function in ansys cfx?

i want to use 450 m/s with overpressure function of blast 0.35 bar and temperature 279 C , can I input it in the inlet of ansys cfx?

and i still dont understand, must i use outlet boundary condition with 0 m/s velocity or using an opening as my outflow?
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Old   March 22, 2015, 07:13
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Quote:
for the inlet boundary i will use sphere with pressure based on some function, can I input the function in ansys cfx?
Yes. Have a look at 1D interpolation functions, or CEL expressions.

Quote:
i want to use 450 m/s with overpressure function of blast 0.35 bar and temperature 279 C , can I input it in the inlet of ansys cfx?
Look in the CFX documentation for the available options for supersonic inlets.

Quote:
must i use outlet boundary condition with 0 m/s velocity or using an opening as my outflow?
You can use any boundary condition you like. As I do not know what you are modelling I cannot assess how suitable the options you list are.

But you cannot define an outlet with 0m/s velocity - then no flow will occur.

If this blast is to occur in a far field then an opening with zero relative pressure makes sense.
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Old   April 7, 2015, 12:20
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dewangga yudistira
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Quote:
Originally Posted by ghorrocks View Post
Yes. Have a look at 1D interpolation functions, or CEL expressions.



Look in the CFX documentation for the available options for supersonic inlets.



You can use any boundary condition you like. As I do not know what you are modelling I cannot assess how suitable the options you list are.

But you cannot define an outlet with 0m/s velocity - then no flow will occur.

If this blast is to occur in a far field then an opening with zero relative pressure makes sense.

thank you ghorrocks
I'm already finished for the model, Im using point of blast as a sphere model


to make it supersonic I must used fluid whose density is a function of pressure, like CH4 or some gas phase hidrocarbon and set the fluid models>heat transfer as total energy right?

for the outlet I still confuse, must I used outlet or opening for boundary condition, for a distance I want to make the pressure and velocity normal


the blast simulation i want to make start from ignite point of blast ( i modelled as sphere) with 450 m/s (supesonic) 1.33 bar pressure and then for some radius the pressure and velocity will be normal


must i using some CEL to define my boundary case?
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Old   April 7, 2015, 22:23
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Your domain looks like minecraft. My kids like blowing things up in minecraft as well

Yes, for a compressible flow you need to use total energy as the heat transfer model.

An alternative to the outlet you can looking at is you can also do this using a source point. This is probably a better way of doing it if you want the explosion to start at a small point.
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Old   April 11, 2015, 03:52
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for the first i want to simulate simple model, if it works i will make it more complicated

I have some reference to do my simulation, but I still didnt understand how to input the parameter, can you help me to understand it ghorrocks? is it neccessary to using CEL to define the parameter?

link
http://journals.ajaums.ac.ir/files/s...-8-252065f.pdf

the simulation using transient analysis, but i dont get it how to generate blast shock wave from the inlet, please help me ghorrocks
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Old   April 12, 2015, 08:50
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I would recommend using a mass source point, not an inlet for this. Give that a try first.
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Old   April 15, 2015, 23:15
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thanks for answer my question ghorrocks

mass source? can you give me more explanation or example?

I still not understand how to set mass source for the inlet
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Old   April 16, 2015, 04:50
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Have you tried the CFX documentation?
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Old   April 16, 2015, 21:55
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I read some of tutorial, which one did you mean?
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Old   April 17, 2015, 06:44
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I do not think any tutorials use source points. The modelling guide and other documentation explains them well.
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Old   April 25, 2015, 09:23
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I'm not too understand at all ghorrock
can we define an expression like this mathematical function for the inlet


with Po=10MPa, and theta 1 ms to get this plot for the inlet


I hope you can help me
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Old   April 26, 2015, 20:33
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The mass source approach requires a mass flow rate to be defined. Your function defines a pressure function. So that function is easy to implement at an inlet, but will require transformation to a mass flow rate if you want to use the mass source point approach.
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Old   April 26, 2015, 23:43
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is that means i need to define mass flow rate as my inlet? I have the information for the mass flow rate


I also want to define the changes of pressure of blast from time
the pressure function that i show you in my last reply will give this kind of result, I read it from dissertation publication


i wonder how can he define the inlet to make this kind of simulation in cfx
any suggestion?
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Old   April 27, 2015, 07:06
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You cannot prescribe BOTH pressure and flow. To do so is a badly posed boundary condition. You can only prescribe one, and then you check the other is what you expect as a check things are working properly.
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