# Reference Pressure

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Hi,

i couldnt find where to define the reference pressure in AcuSolve. There is a Pressure Option at Nodal Initial Condition, but i am not sure how to define the operating pressure for the simulations (for  example atmospheric pressure)?!

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I assume you mean the Absolute Pressure Offset.

Its under the problem description. See screenshot.

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Also check workshop 7 (Natural Convection) and Workshop 8 (Honey in Tea) for other option to define pressure in system, where there is no classical inlet/outlet.

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Thank you so much for the informations, ydigit.

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If the material properties are not dependent on pressure (so constant properties) one only needs to define the properties based on the desired operating pressure.  AcuSolve is essentially computing pressure differences, but where those differences lie on the pressure scale is not important.  If the properties are dependent on absolute pressure, then the values for pressures used for boundary conditions, initial conditions, and for absolute pressure offset become more important.

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Hello,

I have to perform a simulation with air at a pressure of 10 kPa. So should I move the absolute pressure offset to -90000? My simulations wants to calculate the natural covection obtained in these conditions. Also I defined a Far Field with a pressure inlet condition of 10000.

Is my setup well done?

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Are you going to run with density as a function of both temperature and pressure (Ideal Gas), or only of temperature (Boussinesq)?  If only of temperature, then you don't need to be concerned about the absolute pressure at all.  Simply use/define the material property values at the desired pressure of 10kPa.  If properties are also a function of absolute pressure, then you need to use absolute pressure in your BCs.

Personally I always leave absolute pressure offset at 0, and if absolute pressure is necessary, use absolute values for BCs, etc.  Absolute pressure offset essentially means all other pressure values are relative to that stated offset value.

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I run a Boussinesq density model, and with the definition of the nodal pressure the model seems to work well.

So, in conclusion, the absolute pressure offset would be a value that changes the pressure value of the BC's?

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Essentially yes.  The pressure used at the solver level is the pressure stated as a BC, plus whatever value is stated as the absolute pressure offset.  (The absolute temperature offset operates the same way.)

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