Moments and forces in different frames of reference

In summary, the conversation involves a question about calculating values in the center of gravity frame of reference using coefficients obtained from a CFD analysis. There is also a discussion about whether the question should be posted in a different forum and a clarification on the nature of aerodynamic forces. The conversation concludes with a reference to a link for calculating the moment of inertia with respect to a parallel axis.
  • #1
Marco9518
18
1
Good morning!
I know this may sound a little odd, because there is a theorem regarding it, but i have this question.
Basically, a CFD analysis gives me the value of the forces and the moments, as a function of fuselage's orientation, in a particular frame of reference.
How can i calculate the values in the C.G. frame of reference? Forces have no problem, but moments do.
 
Mathematics news on Phys.org
  • #2
Are you looking for the formula for calculating the moment of inertia with respect to a parallel axis? This is a reference.
 
  • #3
FactChecker said:
Are you looking for the formula for calculating the moment of inertia with respect to a parallel axis? This is a reference.
Thanks, but I was talking about aerodynamic forces.
 
  • #4
@Marco9518 -- Is there a different sub-forum where we can move this to where it would be a better fit? Maybe the Aerospace forum or ME forum? Or do you think this General Math forum is still best?
 
  • #5
Marco9518 said:
Thanks, but I was talking about aerodynamic forces.
Aerodynamic forces are in the form of coefficients for the torque in each axis (after proper multiplication by factors). The plane reacts like anything else with the same forces and moments of inertia.
 
  • #6
FactChecker said:
Are you looking for the formula for calculating the moment of inertia with respect to a parallel axis? This is a reference.
Thanks, but I was talking about aerodynamic forces
berkeman said:
@Marco9518 -- Is there a different sub-forum where we can move this to where it would be a better fit? Maybe the Aerospace forum or ME forum? Or do you think this General Math forum is still best?
Hi! i thought about that! I just think that, being this a mathematical/physical problem, would be more helpful to post it here. Do you think it is possible to have it in both sections?
 
  • #7
Marco9518 said:
Thanks, but I was talking about aerodynamic forces
I don't understand. What is it about aerodynamic forces that you think are different from other forces? In my experience, they are treated the same. When you use 6-degree of freedom equations of motion, the aerodynamic forces and moments are combined with other forces like those from the propulsion, gear, gun, gravity, etc.
 
  • #8
FactChecker said:
I don't understand. What is it about aerodynamic forces that you think are different from other forces? In my experience, they are treated the same. When you use 6-degree of freedom equations of motion, the aerodynamic forces and moments are combined with other forces like those from the propulsion, gear, gun, gravity, etc.
So, basically i need to validate a simulink model that gives me forces and moment acting on the fuselage of an helicopter, given speed, angle of attack and angle of sideslip. There are no rotors, no appendices, nothing but the fuselage. The model needs some coefficients. The CFD analisys gives me forces and moment in a particular frame of references. I need to calculate the same forces and moments in another frame of reference which has its reference pole in the center of gravity.
 
  • #9
FactChecker said:
Aerodynamic forces are in the form of coefficients for the torque in each axis (after proper multiplication by factors). The plane reacts like anything else with the same forces and moments of inertia.
This forces are not in form of coefficient. What i have is for example: at 0 deg of angle of attack the Fx is 5N, at 15 deg is 20N and so on.
 
  • #10
Marco9518 said:
Do you think it is possible to have it in both sections?
No, sorry.
 
  • #11
Marco9518 said:
This forces are not in form of coefficient. What i have is for example: at 0 deg of angle of attack the Fx is 5N, at 15 deg is 20N and so on.
That just removes a slight complication. A force is a force is a force. The only thing that changes is the measurement of the reaction to the force when a different axis of rotation is used. That changes the moment of inertia as described in the link I referenced in post #2.
 

1. What is a moment in physics?

A moment in physics is a measure of the tendency of a force to cause an object to rotate about a specific point or axis. It is calculated by multiplying the magnitude of the force by the perpendicular distance from the point or axis to the line of action of the force.

2. How do moments and forces differ in different frames of reference?

In different frames of reference, the magnitude and direction of moments and forces may appear different due to the relative motion of the observer. However, the physical effects of these moments and forces, such as rotation or translation, will remain the same.

3. What is the difference between a moment and a torque?

A moment is a general term used to describe the turning effect of a force, while torque specifically refers to the turning effect of a force around an axis. Torque is a type of moment that is applied in a rotational motion.

4. How do moments and forces affect the stability of an object?

Moments and forces can affect the stability of an object by either causing it to rotate or keeping it in a state of equilibrium. A larger moment or force acting on an object can cause it to become unstable and change its position or orientation.

5. Can moments and forces be balanced in different frames of reference?

Yes, moments and forces can be balanced in different frames of reference. This means that the sum of all the moments and forces acting on an object is equal to zero, resulting in a state of equilibrium. However, the individual magnitudes and directions of these moments and forces may appear different in different frames of reference.

Similar threads

  • Special and General Relativity
2
Replies
51
Views
2K
  • Special and General Relativity
Replies
23
Views
575
  • General Engineering
Replies
18
Views
1K
  • Special and General Relativity
5
Replies
144
Views
5K
Replies
25
Views
1K
Replies
1
Views
783
  • Introductory Physics Homework Help
Replies
34
Views
912
  • Special and General Relativity
Replies
7
Views
811
Replies
19
Views
1K
  • Quantum Physics
Replies
10
Views
964
Back
Top