Q. FAQ - Local axis for AutoPIPE Pipes and Beams


This article will answer questions related to AutoPIPE's local axis directions. Users should have already reviewed AutoPIPE's help section on "Local Axis Option: Straight Pipe Forces and Moments" (AutoPIPE help section: Help ribbon> Contents button> Contents Tab> Reference Information> Results Interpretation> 

 

In addition, users should already know about AutoPIPE's feature to show local coordinate indicators (View > Display Axes > Local Axes > Local Axes)

FAQ:

  1. Local axis orientation for an inclined/non-vertical straight pipe
  2. Understanding Local X and Z plane for inclined pipe
  3. Understanding Local Y and Z plane for different scenarios
  4. Explaining the local-axis convention for Tee and Bend components
  5. How to define a User's local axis? 
  6. Local axis directions when +Z-axis is vertically up

Question #1:

Confirm our understanding of the local axis orientation for an inclined/non-vertical straight pipe in AutoPIPE, specifically when reviewing straight pipe forces and moments using the Local Axis option.

Assumption:

Vertical longitudinal / vertical axial plane

 

The vertical longitudinal plane is defined as:

Since Global Y is the vertical/up direction in this case, this becomes:

For an inclined pipe, local y lies in this plane, is perpendicular to local x, and points generally upward.

Therefore:

Vertical longitudinal plane = local x–local y plane

Answer: 

To answer a question like this, suggest starting a new model in AutoPIPE, model this pipe and turn on the Local Axis as mentioned above. 

Yes, the assumption is correct, for an inclined pipe, local Y-axis lies in this plane, is perpendicular to local x, and points generally upward (as imaged above).

(top)

Question #2:

Horizontal longitudinal / horizontal-side axial plane

The horizontal-side longitudinal plane is defined as:

This plane is normal/perpendicular to the vertical longitudinal plane while sharing the same local x axis.

For an inclined pipe, we understand that this plane is not truly horizontal as a whole, because local x is inclined. Only local z is horizontal.

Answer: 

Again, build a model with piping in multiple orientation to help address this question and turn on the Local Axis as mentioned above. 

No, the assumption is not correct, for an inclined pipe, local Z-axis is always parallel Global X-Z plane (imaged above).

(top)

Question #3

Cross-sectional / transverse plane

The cross-sectional plane is defined as:

local y–local z plane

This is the plane normal to local x and represents the pipe cut-face plane.

We would also like to confirm the following specific cases:

Case 1:

If the pipe lies in the Global X–Global Z plane, and Global Y is vertical, then the pipe is horizontal.

local x is along the pipe direction inside the Global X–Global Z plane.

The vertical longitudinal plane is:

plane(local x, Global Y)

Therefore:

local y = Global Y

Answer:

Yes, anytime the pipe is flat on horizontal plane, one could always say the local Y-axis is always vertically Up. Because, local X-axis and local Z-axis make up the horizontal plane, argo normal to the Global / Local X-Z plane is the Local Y-axis / Global Y-axis.  

Yes, whenever the pipe lies flat on a horizontal plane, it can be asserted that the local Y-axis is consistently oriented upwards. This is due to the fact that the local X-axis and local Z-axis constitute the horizontal plane (Global X-axis & Z-axis; therefore, the normal to the this plane is represented by the Global Y-axis which coinisides with the Local Y-axis.

(top)

Case 2:

If the pipe lies in the Global X–Global Y plane:

local x is along the pipe direction inside the Global X–Global Y plane.

The vertical longitudinal plane is:

Global X–Global Y plane
= local x–local y plane

Therefore:

local z is normal to that plane
local z = Global Z

Answer:

The answer is identical to that provided in case 1. Referring to an example model featuring a pipe oriented at any angle on the Global X-axis and Global Y-axis plane, there exists only one axis direction that remains perpendicular to this plane for all pipe angles, which is the Global Z-axis. In this scenario, it aligns with the Local Z-axis.

(top)

Case 3:

If the pipe lies in the Global Y–Global Z plane:

local x is along the pipe direction inside the Global Y–Global Z plane.

The vertical longitudinal plane is:

Global Y–Global Z plane
= local x–local y plane

Therefore:

local z is normal to that plane
local z = Global X

Answer: 

The response is the same as that demonstrated in case 2; the only distinction is that the pipe is rotated 90 degrees on the horizontal plane. A rotation of 90 degrees relative to the Global Z-axis and Global Y-axis corresponds to the Global X-axis, which aligns with the direction of the local Z-axis.

(top)

Question #4:

Could you please provide AutoPIPE reference/documentation explaining the local-axis convention for Tee and Bend components?

Answer: 

Please see the top of this article for information to help answer this question

See AutoPIPE help> Results Interpretation>:

(top)

Question #5:

How to define a User's local axis? 

Example: if my pipe is going in X dir at anchor and I want to define local axes 45 deg. horontal to X-axis, is there a way? 

Answer: 

No. AutoPIPE establishes the local axis according to the segment direction (from upstream to downstream), the orientation of the piping relative to global coordinates, and the vertical axis direction specified in the General Model Options dialog.

Users are not permitted to define their own local axis direction.

(top)

Question #6:

What are the local axis directions when +Z-axis is vertically up in AutoPIPE?

Answer: 

See KB article here. 

(top)