Pressure load

[christophersrikanth]

Hi-I asked this question in another discussion group on eng-tips but was advised to post here instead -I did not get satifactory replies in the that group (NX-UG) as well

I have just been reading the tutorial in NX (as well as practising doing it) concerning pressure loads in NX.

Now, if you recall the definition of pressure (

http://wiki.answers.com/Q/Why_pressure_is_scalar_quantity_where_as_force_is_vector_quantity)

we see pressure is a scalar.

This is clear.

However, in NX if we go to load type->PRessure, in the dialog box, there is also an option of defining the components of pressure.

My question is, how can pressure ahve a unique direction?

Sorry for a very fundamental question-please note this is not a homework question but very much a question from me- working on real problems.

 

[rb1957]

it's quite common to applied load distributed over an area, thus a pressure (obviously directional).

in most cases you should see pressure as normal to the surface, thus scalar.

i guess NX is saying if you have an inclined load on the surface, that you want to distribute over an area then you's have normal and in-plane components; yes?

Quando Omni Flunkus Moritati

 

[corus]

Pressure can have a direction if, say, you're looking at the thermal expansion of a lining on a pressure vessel, which has an inclined surface, ie. is conical. In such a case you'd normally have to apply a pressure normal to the surface and then add in another shear component to get the required pressure distribution.

 

[christophersrikanth]

rb1957

In that case (applied load distributed over an area)- it is strictly 'not' pressure, it is a distributed traction.

Strictly going by the definition of pressure, it acts in all directions and is described by the magnitude alone.

 

[rb1957]

to me that's semantics ... force over area = pressure

Quando Omni Flunkus Moritati

 

[rb1957]

thinking about it, hydro-static pressure is omni-directional and scalar.

force over area will have a direction (force is a vector)

Quando Omni Flunkus Moritati

 

[IDS]

I think the link is misleading.

Definition from Wikipedia:

"Pressure is force per unit area applied in a direction perpendicular to the surface of an object"

If the "surface" does not have a defined direction (such as for pressure at a point in a fluid) then pressure is a scalar.

If the surface does have a defined direction (such as for pressure applied to a surface in a finite element analysis) then pressure is a vector.

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/