Dynamic Vibration Absorbers

[@famine784]

This video has taught me more in 27mins than my final year university vibration control professor has in 6 months. Thank you for the clear presentation and detailed explanations!

[@hannurissanen9971]

I'm going to use this theory on my working immediately. Thank you very very much.

[@Unplannedmoves]

Loved your Knowledge sir and the way you imparted into us.

[@yahyasheikhnejad]

very nice explanation and thank you for your time. I enjoyed it a lot.

[@AJ-et3vf]

Great, insightful video as usual. I particularly like and appreciate you pointing out what X2k2 = -Fo physically means, specifically that it means that k2 exerts a force on mass m1 equal to Fo which is why the the displacement would be zero. That didn't occur to me why the first time. I just thought that it's a nice, short formula compared to that of X1. Really appreciate these videos and this channel. Very helpful.

[@muhammadahsan3526]

Great video, really appreciate the work.

[@umutsenol2894]

good explanation, thanks from Turkey

[@ammarburhani8328]

Super good explanation. Good work bro.

[@abdullaabbadi7212]

Very good,Vert beneficial

[@hayden9944]

Great video - all lectures should do this digitally and clearly like this... One question, Omega = Omage1 = Omega2. If i was to add mass to the table it wont change Omega because this is the frequency of the motor... but it will change the mass term in the equation SQRT(K1/m1), which will change Omega1. I am an engineer and having to dive into a field I haven't looked at for 10 years! Your help would be appreciated!

[@ticheroi]

As always very understandable, informative and interesting)

[@cedericcallens9053]

If you have a 10 storey building subjected to a wind load, what will be the difference in hanging this secondary mass on 1st, 5th or 10th floor? (Great video)

[@Freeball99]

In buildings, a tuned mass damper is typically located towards the top for maximum effect. Also, sometimes slosh tanks are used (which go on the roof).

[@stitaswain7349]

great sir ... thank you for the awesome video

[@justincontreras7662]

Your videos are awesome. Are you a professor/lecturer?

[@Freeball99]

Thanks for the feedback... No, I'm not a professor. I spent many years in graduate school and, along the way, I was the teaching assistant for the Introductory Mechanical Vibrations class...several times. I held weekly recitation sessions with students and lectured at review sessions prior to exams. When helping students, it always struck me that this material was never taught well and this left many of them confused.

[@yogisetiawan8982]

@Freeball99 let say if we have vertical tower to damp where the base of tower have been fixed with the ground, what is means by M1? Is it entire mass of tower? (Just try ti make analogy to solve something in my system). Thanks

[@Freeball99]

As a first iteration, if we assume that we have a vertical cantilevered beam and we are examining deflections at the tip, then the equivalent mass at the tip would be 1/3 the total mass of the beam.

[@dereck-2205]

beautiful

[@정재덕-x1k]

I think, It seems that the impedance matrix you mentioned is the dynamic stiffness matrix. Is that right?

[@Freeball99]

Yes, these are the same thing.

[@johnymacgyver3554]

Thank you freeball, very understandable for describing equations from the book. may i ask? if i were to make a model of vibration absorber like this, i could have known the value of m2 i give to the system, but how could i calculate the value of k2 to assure me that the mass2 will definetly neutralize the response of the main system (X1)? and is there a way for adjusting stiffness for the vibration absorber? thank you, sorry for bad english

[@Freeball99]

Sorry for the delayed response, but I somehow missed your message until now.. I'm not sure if I understand you question exactly, but hopefully my answer will cover it... In this simple case, you would know the value of k2 (you could measure it in a lab by applying a force and measuring the corresponding displacement). Most likely in a real-life situation, you will likely pick the spring first and tailor the mass accordingly since it might be easier to finely adjust the mass instead of the spring. Hope this helps.

[@johnymacgyver3554]

@@Freeball99 thank you for the answer, it really helps me a lot. Thanks!

[@fabiozangoli5107]

Very nice. Gave exactly info I was looking for. Thank you and a question: what tablet did you use for your presentation?

[@Freeball99]

iPad Pro 13 inch and an Apple pencil.

[@fabiozangoli5107]

@@Freeball99 thx

[@JoakimStenudd]

Great video, very much helpfull. But one question, is there a way to go the other way around, to cancel out the movement of mass 2 with mass 1? When looking at the eq. 15 and 16 it looks impossible because the numerator is 1 in eq 16. I understand that the purpose of mass 2 is to absorb vibration from mass 1 but lets just imagine for a second we have a 2-dof system and try to achive this.

[@abraiz2221]

Where can I find the mathematics behind the damping of a pendulum type tuned mass damper with explanations? Not a spring-mass one

[@Freeball99]

It's called a pendulum tuned mass damper. Here's an example of how to derive equations of motion (a few pages in). engineering.purdue.edu/~ce573/Documents/Intro%20to%20Structural%20Motion%20Control_Chapter4.pdf

[@alieltair5418]

Hello, thank you for this it was very helpful. Is there any way I can get some sort of formal citation to reference it for an essay I am writing?

[@Freeball99]

Actually I had to Google this. Apparently the correct way to cite a KZbin video is this... Friedman, Andrew. "Dynamic Vibration Absorbers." KZbin, uploaded by Freeball, 25 May 2017, kzbin.info/www/bejne/bYWZoYSkg6ejnpI

[@alieltair5418]

@@Freeball99 Thank you so much 👌

[@ilyagordievsky9530]

Hello. Could you please help me. I want to design Dynamic Vibration Absorber for 25Hz. I am looking for methods. Do you know where can i write ot watch about how to design it?

[@Freeball99]

1️⃣ Determine primary system parameters: • Mass (M₁) and stiffness (K₁) • Ensure natural frequency is 25 Hz 2️⃣ Choose absorber mass (M₂): • Typically 5-20% of M₁ • Consider practical constraints 3️⃣ Calculate absorber stiffness: • K₂ = M₂ * (2π * 25)² • Tuning condition: K₂/M₂ = K₁/M₁ 4️⃣ Consider adding some damping for better performance 5️⃣ Verify by plotting frequency response

[@absorbit8]

Thank you ​@@Freeball99

[@ninepuchar1]

May I ask if For [Z], should the 1st row,2nd cloumn be Z(12) instead of Z(21)?

[@Freeball99]

Yes, you're correct. However, the [Z] matrix is symmetric, therefore Z12 = Z21

[@ninepuchar1]

@@Freeball99 thank you🙏

[@omarkhalil4676]

Thanks a lot !!

[@Hudmyq]

Hi, Freeball, It's me again. Thanks for your video. I'm working on the vibration absorber recentely. Based on equation 1 and 2, I have designed a simulink program to investigate the displacement of m1. However, as your conclusion shown on the end of your video, the displacement m1 isn't zero when the excitation frequency is equal to natural frequency of m1 and natural frequency of m2. Is it matlab problem ? or do we miss something here ?

[@Freeball99]

I believe the math to be correct - displacement should be zero (although I've been known to make errors before). Personally, I've never tried to implement this simulation mathematically so I can't comment on an potential pitfalls to avoid. While I am not a MATLAB guru (I prefer Mathematica or Python/Numpy), I'd be happy to take a look at what you have if you want to forward it to me at [e-mail] - perhaps I can offer some suggestions.

[@vp1788]

it was amazing. thank you so much. Do you have the Matlab code for the system?

[@Freeball99]

Are you referring to the chart I show at 25:49 ? Are you looking for the code for that produced this?

[@vp1788]

Freeball Thanks for the reply by the way

[@Freeball99]

The video that I linked to (in the description) is not one of my videos. I have no affiliation with that person so unfortunately I don't have the MATLAB code....besides I'm a Python/Numpy guy anyway, I always found MATLAB to be too expensive once I left school :o)

[@lignedroite5806]

@@Freeball99 Can you share with us the python code ?

[@reddyramu2482]

what happens if the secondary mass is greater than the primary mass

[@Freeball99]

There is no restriction on the relative sizes of the masses - so if the mass is heavier, you'd need a stiffer spring to get a tuned response. Typically, however, when examining the problem at hand, we usually have a piece of machinery or a structure that is exhibiting an undesirable response. Typically, we want to reduce vibrations by adding a much smaller mass since adding a very large one might be impractical. So, the restriction has more to do with the physical geometry of the problem rather than vibration theory. Clearly, in the case of a building, it makes no practical sense to add a secondary mass that is heavier than the building.