Talk:Mechanical impedance

Untitled

Isn't the change in air pressure due to noise causing a movement of particles in the air that will hit a structure thereby causing a net force? What is all this talk of force-like?Porco-esphino (talk) 11:23, 23 August 2009 (UTC)

Restructuring needed

This article has four sentences starting with "Mechanical impedance is" which each gives its own definition! The text needs restructuring of the otherwise correct and clearly written sentences. Ovikholt (talk) 18:42, 3 January 2012 (UTC)

Example impedances

It might be good if the article listed some example materials and their frequency dependent impedances through functions or illustratory graphs. Ovikholt (talk) 18:45, 3 January 2012 (UTC)

Wrong definition

The Mechanical impedance definition is wrong. Instead of the speed-vector v(w) with dimension of [m/s], it should be used the 3D-speed vector with dimension of [m^3/s]. That is because the speed is related to a 3D-particle. Then the dimensions of both, the Mechanical impedance and the Specific Acoustic impedance, will be equal to [a/m^4]. — Preceding unsigned comment added by 76.91.214.254 (talk) 05:33, 4 December 2012 (UTC)

This sounds like a very specific application. The definition in this article is not wrong, so maybe you should include a source. 81.62.106.234 (talk) 13:03, 29 March 2013 (UTC)

Source

In the book ,,Robotics and Automation Handbook,, , edited by Kurfess, it is explained what impedance is. In Chapter 19 it's defined as Force over velocity. Further you can also refer to Hogan's Paper from 1985 ,,Impedance Control: An Approach to Manipulation,,.

81.62.106.234 (talk) 13:00, 29 March 2013 (UTC)

harmonic

I understand the ratio of force to velocity, but I don't know why it needs to be harmonic. It is convenient for electrical impedance to consider it a function of frequency, but that isn't required. I am now looking at Turbofan which uses a turbine to convert a high velocity flow from combustion into a lower velocity flow. This is equivalent to impedance matching, as much of the power is otherwise wasted, similar to impedance mismatch in electrical, and other mechanical systems. Gah4 (talk) 00:06, 25 May 2022 (UTC)

Linear increase with time? Or periodic after all?

The current article text contains:

"Mechanical impedance is the ratio of a potential (e.g. force) to a flow (e.g. velocity) where the arguments of the real (or imaginary) parts of both increase linearly with time."

I have trouble understanding the "linear increase with time" part, in light of the mention elsewhere in the text that (mechanical) impedance is defined for periodic forces or cases. What am I missing?Redav (talk) 13:33, 27 May 2022 (UTC)

It seems convenient to compare to electrical impedance. A constant electrical impedance means one (mostly) not dependent on current and voltage. In this case, it should be that the force/velocity is close to constant as force and velocity change. In the electrical case, you can take the frequency dependence and the Fourier transform to apply it to any time dependence, but it is most useful when it is close to frequency independent. I was reading Turbofan where the bypass ratio allows one to change the thrust/exhaust velocity to more closely match the desired air speed. That is, mechanical impedance matching. But airplanes don't normally fly with periodic speed. They do vary velocity and engine thrust, though. Gah4 (talk) 17:39, 27 May 2022 (UTC)

characteristic impedance

Mechanical impedance should have a good analogy with the (usually electrical) characteristic impedance. Impedance is most useful when it is (mostly) independent of frequency, and so more characteristic. A wave on a violin string is well characterized as a mechanical impedance, for example, in analogy to an electrical wave on a coaxial cable. Gah4 (talk) 11:59, 1 June 2022 (UTC)

In one respect, characteristic impedance is even more significant in mechanical systems. This is because the lumped-element model fails at a much lower frequency than it does in electrical systems. There is something on this at Mechanical filter#Semi-lumped designs. I guess the reason we don't hear more about it is that mechanical components rarely have a constant cross-section in the z direction over a significant distance like an electrical cable does. SpinningSpark 09:26, 5 June 2022 (UTC)

OK, back to this one again. The article uses the resistive/reactive parts, like electrical systems, but misses the real part for a propagating wave, either down a transmission line or violin string. Though as you note, the strings aren't as long as coaxial cables. Gah4 (talk) 04:06, 5 December 2022 (UTC)

Since the article is not discussing travelling waves at all, it is not surprising that this is not found here. I'm not sure that this article is the right place for that discussion in any case. Compare electrical impedance where it also is not discussed. SpinningSpark 13:43, 5 December 2022 (UTC)

Strangely, characteristic impedance on my watch list got edited at almost the same time, and so I am thinking about both. But also, I tend to think about them together, though the cause is different. I got here, if I remember, related to discussion in an article about jet engines, and fluid flow. It doesn't need to be in electrical impedance if it is in characteristic impedance (and hopefully appropriately linked). But then which article discusses characteristic impedance for mechanical systems? Gah4 (talk) 23:41, 5 December 2022 (UTC)

I just did a search for sources. This looks more interesting than I first thought. I might write something in the next few days. SpinningSpark 13:21, 6 December 2022 (UTC)

I'm going to retract from doing that. I'm not seeing a lot on mechanical characteristic impedance for impedance as defined here. I'm sure such a thing exists, but we could do a lot of searching and just come up with a not very interesting definition. The interesting sources I found were actually talking about characteristic impedance in acoustics and fluid flow. In these field the analogies are force/pressure and velocity/vol flow rate, so impedance is defined as P/Q, not F/v. Consequently, characteristic impedance is a property of a material, not of a component as it is in mechanics. So in my opinion, it would be wrong to try and shoe-horn it in here. SpinningSpark 18:56, 8 December 2022 (UTC)

You can do the F/v impedance in, for example, a wave on a taught string. If you have a discontinuous mass per unit length, there will be a reflection, just like on a transmission line. These problems are favorites in physics. But yes, it is the P/Q form that I was wondering about, in the explanation for the High-bypass turbofan engine. It is more efficient to have the jet exhaust closer to the speed of the jet, for the same reason as electrical impedance matching. I am not sure about the property of the material, though. You want high velocity for a supersonic jet fighter, and not so high for the usual passenger jet. (And mostly not the transmission line type impedance.) Gah4 (talk) 23:00, 8 December 2022 (UTC)

As I said, I know this analogy exists. I've written some relevant material at Mechanical filter#Semi-lumped designs and Mechanical–electrical analogies. As I've also said, I'm not going to write something myself for the lack of interesting sources to base it on. But feel free to do something yourself. SpinningSpark 10:37, 10 December 2022 (UTC)

tensor

The article seems to mention force and velocity in the same direction. It seems that in the usual case, there should be a tensor between force direction and velocity direction, such that it might not go in the same direction. Gah4 (talk) 04:08, 5 December 2022 (UTC)

Completely agree with that. SpinningSpark 13:30, 5 December 2022 (UTC)

Under the scope of WikiProject Robotics?

It seems that this topic has many applications in robotics and engineering, would it fall under the scope of either of those wikiprojects? I think it would get more attention and contributions if it is in the scope of robotics, as it would likely have a higher importance there. However, I do not know what I am doing or how to do it, and may be completely wrong. 2001:569:5826:C800:8154:EA12:F9B2:4B46 (talk) 20:49, 8 October 2023 (UTC)

I've added it to the robotics project ~Kvng (talk) 23:15, 11 October 2023 (UTC)