Calculating surface normal vector

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    Normal Surface Vector
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Discussion Overview

The discussion revolves around calculating the normal vector for a surface, specifically for surface F, in order to determine the velocity component for U. Participants are exploring methods to derive the normal vector, including the implications of angles and coordinate systems.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant seeks guidance on calculating the normal vector Nf for surface F to find the velocity component for U.
  • Another participant suggests that the normal vector may not be necessary and proposes that the normal component of U can be calculated using the angle θ between Nf and U, expressed as Ucosθ.
  • A different participant points out that without specific coordinates or angles, it is impossible to calculate an absolute normal vector, but suggests choosing a convenient coordinate system where the normal vector could point along the positive x-axis.
  • One participant emphasizes the need for a formula to calculate the unit normal vector for surface F given any angle.
  • Another participant requests clarification on how surface F is defined and whether there is a specific example to consider.
  • A later reply indicates that the discussion includes a detailed picture and mentions the need to calculate the unit vector for surface E at an angle θ in a 2D Cartesian mesh.

Areas of Agreement / Disagreement

Participants express differing views on the necessity of the normal vector and the methods to calculate it. There is no consensus on how to proceed, as multiple competing approaches and uncertainties remain in the discussion.

Contextual Notes

Participants have not provided specific definitions for surface F or surface E, nor have they clarified the coordinate systems in use. The discussion includes unresolved questions about the angles and the relationship between the vectors involved.

Who May Find This Useful

This discussion may be of interest to individuals working on vector calculations in physics or engineering, particularly those dealing with surface normals and velocity components in various coordinate systems.

andykol
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Hello,
I am trying to calculate normal vector for surface F Nf (see attached picture) to calculate velocity component for U. I tried to get more info but got confused.
Please tell me how I can calculate Nf.
Thanks in advance.
 

Attachments

  • Vector.JPG
    Vector.JPG
    3.1 KB · Views: 664
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Welcome to PF!

Hello andykol! Welcome to PF! :smile:
andykol said:
I am trying to calculate normal vector for surface F Nf (see attached picture) to calculate velocity component for U. I tried to get more info but got confused.

I'm not sure what you're asking :confused: …

you don't need the normal vector …

to calculate the normal component for U, all you need is the angle, θ, between Nf and U …

the normal component of U is simply Ucosθ. :wink:
 
More information is necessary. In any coordinate system, a vector normal to another vector has a dot product of 0 with that vector. In 2 dimensions, this simplifies to the normal vector having the negative reciprocal slope of the vector it is normal to. you haven't given two-dimensional coordinates to the points, nor angles, so there is no way to calculate an absolute normal vector, but if the problem does not relate to any particular coordinate system (ie., there is no potential field; gravity, electromagnetism) then choose a convenient set of coordinates; ie., let that rectangle be horizontal with vertical sides; then the normal vector points along the positive x-axis. You still need the angle between F and N.
 
Thank you for reply.

But I need to calculate unit normal vector for surface F. I am looking for formula that calculates normal vector of surface with any given angle.
 
andykol said:
But I need to calculate unit normal vector for surface F. I am looking for formula that calculates normal vector of surface with any given angle.

Sorry, I still don't understand :confused: …

how is F defined?

do you have a particular example in mind?
 
Hello tiny-tim,

I have attached detailed picture. I have to calculate unit vector for surface-E Ne. For given Cartesian coordinates, how I can calculate surface normal?
E.g. 2D Cartesian mesh- I got surface-E at an angle θ.
 

Attachments

  • Vector.JPG
    Vector.JPG
    5.1 KB · Views: 700
Last edited:

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