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Blade Performance Vs Wood Type and Design |
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24prozent
Beginner Joined: 02/15/2008 Location: France Status: Offline Points: 11 |
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Posted: 11/06/2022 at 12:26pm |
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Hi JRSDallas!
I enjoyed your deep treatment of the physics of the blade, and I also want to thank HEX for his contributions; even though the discussion between the two had taken on at some instances a highly competitive and confrontational nature. I have a somewhat naive question and a comment. Can you make it plausible to me why the blade has a very noticable impact on the playing properties, given that it is covered by a rather thick rubber? Seeing the very different rebound velocities of a ball from just wood and from rubber coated wood, I would expect that the rubber has a much bigger impact than the blade itself. And my "prejudice-soaked intuition" would conclude the same, i.e. that the blade properties are "buried" under the rubber properties. And yet I do know from own experience how a blade changes the playing properties. Can you enlighten this a bit? You had posted an excerpt from an article that concluded that the racquet/ball contact time would be 4-5 milliseconds, while in your argument with HEX, he claimed that the interaction time is rather 1ms. Before I had read your discussion I had studied this paper: https://www.researchgate.net/publication/305080758_Non_Linearity_of_the_BallRubber_Impact_in_Table_Tennis_Experiments_and_Modeling and from analyzing the stroboscope pictures I came to the conclusion that the contact time is indeed just about 1 ms. How certain are you about the result in the paper that you cited? Would you mind looking at the stroboscope images and giving your feedback on this with respect to ball interaction duration? Ah, and one more thought/question: In an article by Daniel A. Russell on vibro-acustical properties of a table tennis racquet ( https://www.tandfonline.com/doi/full/10.1080/02640414.2018.1462578 ), or his video ( "Acoustics of Ping-Pong" - Dr. Daniel Russell, Penn State University - YouTube https://www.youtube.com/watch?v=ekalYkdrwI8 ) I think the conclusion in a passing comment was that the ball playing (or rebounce) properties did not depend notably whether or not the ball was bouncing off of locations on the blade that were vibrational nodes. I would conclude, that vibration cannot really be the determinator of the rebounce. What -if anything- is wrong about the notion? Ha! And here is one more question: My reading about balsa properties, and the fact that it is used e.g. by TSP (now Victas) in a "cross cut" configuration, where the grain direction is perpendicular to the plane of the verneer, gave me the impression that there might be a compression/vibration/elasticity component of the blade that comes into play. Somewhere else it was described as a spring force by the compression of the blade material, which was mentioned to be particularly effective/elastic in balsa in the direction of the grain/fibres, ...and hence the "cross cut" / "endgrain" configuration. Do you have any thoughts on that? Sorry, as I am writing, more topics come into my head: What are your thoughts about the blade impacting the spin-generation potential of a racquet? The company Re-Impact ( www.re-impact.de ), whose racquets I really like, makes such claims. I have always discarded them as marketing hokus-pokus; but the deeper I dig into the physics of the ball/blade interaction the more I realize how little I understand. Any thoughts on this? |
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adyy
Member Joined: 11/21/2018 Location: in the Lab Status: Offline Points: 25 |
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@ JRSDallas - I tried to replicate your XLS table from this picture with formulas embedded
for the column Moment of Area Ik if I try to calculate it via this formula: Now the moment of inertia I for a beam with rectangular cross section of width b and height h, is given by I = b h3/12. When this cross section is not at the center of the beam (such as will be the case with all but the center ply in our laminate table tennis blade), the Parallel Axis Theorem lets us calculate the moment of Inertia of each ply. Thus the moment of inertia I k for the kth ply is then: I k = b h3/12 + bh d 2 where d is the distance from the midplane to the center of the kth ply. the only way I can match your values from Layer Dist dk and Tickness hk column is using 254 for b. Can you share your XLS? Or was this the formula you used?
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zeio
Premier Member Joined: 03/25/2010 Status: Offline Points: 10833 |
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So that EJs alike would understand when their skills are the problems, no equipment could ever remedy that.
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Viscaria FL - 91g
+ Neo H3 2.15 Blk - 44.5g(55.3g uncut bare) + Hexer HD 2.1 Red - 49.3g(68.5g 〃 〃) = 184.8g |
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wanhao
Super Member Joined: 07/14/2014 Location: south east asia Status: Offline Points: 122 |
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So with all this MIT STANDARD thesis..how can we improve our skills ?
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Baal
Forum Moderator Joined: 01/21/2010 Location: unknown Status: Offline Points: 14336 |
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The guy knows his stuff!
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zeio
Premier Member Joined: 03/25/2010 Status: Offline Points: 10833 |
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Last Visit: 01/12/2016 at 5:44am
I actually have a question or two for him. |
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Viscaria FL - 91g
+ Neo H3 2.15 Blk - 44.5g(55.3g uncut bare) + Hexer HD 2.1 Red - 49.3g(68.5g 〃 〃) = 184.8g |
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arg0
Platinum Member Joined: 07/22/2009 Location: Germany Status: Offline Points: 2023 |
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I noticed the images on the first page have disappeared due to licencing of the hosting service.
But I had saved them, so here they are again: BTW, is JRSDallas still around? |
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AgentHEX
Gold Member Joined: 12/14/2004 Location: Yo Mama Status: Offline Points: 1641 |
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The main point is that if you sand/plane to the point where it's already the right speed/freq/thickness/etc, going past it isn't going to help. For the instrument makers, they're mostly slowly going to the right point, which is a lot more subtle in their case since it's along one dimension. |
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AgentHEX
Gold Member Joined: 12/14/2004 Location: Yo Mama Status: Offline Points: 1641 |
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I see my misconception about your equation, and I edited the post like an hour ago.
> (OK tell us all exactly what is an object's "inherent" vibrational frequency? I know what it is but it has nothing to do with this topic. There's one freq per your own formula and many possible speeds depending on place of impact. This is quite relevant to the topic of whether freq is representative of speed: this is clearly a way it's not. > Please accept my apologies, I had you confused with someone that also goes by the name AgentHEX on the One of a Kind Forum. Can you point to where this happens?: "Still your language shows that you still confuse frequency and blade stiffness as being explicitly linked to blade speed or ball impact COR when in fact the linkage one of reducing energy losses which effects COR due to transfer of impact energy to vibration modes of the blade" I thought I was quite explicit about energy loss above. > So please explain how does moving a blade faster and faster violate physics? A ball which rebounds faster than it impacts the blade violates physics. Look, if you just said that the inertia's for the component slices of beam stiffness and not blade as a whole this would've been a lot easier. The way the integral's calculated for this specifically is not obvious from looking at the result (nor is it mentioned in your prior post). You should be able to see how someone isn't aware of this detail would think the way inertial is being used is wrong. It's plainly obvious the points of contention here are largely conceptual so it's unclear how greater technical detail of, say, how to make freq calc slightly better helps in any case. How exactly does actually taking the enormous amount of time to create a sim advance the point about timelines? Also, if you're familiar with academia this sort of contentious disagreement shouldn't even be unusual. The only difference is I personally didn't care to be passive aggressive about it. |
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Baal
Forum Moderator Joined: 01/21/2010 Location: unknown Status: Offline Points: 14336 |
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I still have no idea what you are talking about. Oh well. In any case, with table tennis blades, they are mass produced in a factory and if you are lucky, you get a really good one. |
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JRSDallas
Silver Member Joined: 09/03/2005 Location: USA Status: Offline Points: 585 |
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Edited by JRSDallas - 01/01/2015 at 10:34pm |
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Galaxy T1 89 gm
FH: HRT Huaruite Wujilong 2 - Dragon 2 II, Max, Black Donic Acuda S2, Max, Red |
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AgentHEX
Gold Member Joined: 12/14/2004 Location: Yo Mama Status: Offline Points: 1641 |
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The original comment was that they stop when it sounds right. The point is going much further than the basic well defined vibrational tendencies of the instrument is just going to sound wrong. Technically all sound is a composition of pure sine waves, which is why a freq-codec + speaker can reproduce all sounds within reason. |
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AgentHEX
Gold Member Joined: 12/14/2004 Location: Yo Mama Status: Offline Points: 1641 |
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Ok, I see what's going on and I'm wrong on that point.
> There is also the issue of your gloat post that followed your careful explanation but was removed by the moderators. You mean this "removed" post?: http://mytabletennis.net/forum/forum_posts.asp?TID=60725&PID=845339&title=blade-performance-vs-wood-type-and-design#845339 > Both can be true if you use the right equation in the right circumstance. No, a given object has an inherent vibrational frequency, even using your own solution type. So which side is this frequency/"speed" for in an asymmetrical blade? > Many people tried to explain this to you on the One of a Kind Forum as well, but to no avail. You have me confused with someone else, so please argue whatever this point is with them and not me. > Uh oh, it looks like the rebound speed of the ball vball’ approaches infinitiy when the blade speed approaches infinity! Yes, that's why we're using a ratio for speed. The COR ratio also happens to be the correct one for measuring blade "speed" since it cannot excel the limit without violating physics. Honestly I expected better from someone who can at least look up the equation above. For example, it was explained why a sim should be considered instead of just static calcs (to establish a correct timeline which is easy to forget when using time-invariant equations). Or what the shape (ie. order) of an equation means, which is a pretty fundamental consideration whenever math is put to science. None of this is remotely difficult to grasp for the technically adept. Edited by AgentHEX - 01/01/2015 at 9:56pm |
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Baal
Forum Moderator Joined: 01/21/2010 Location: unknown Status: Offline Points: 14336 |
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I can't figure out what point this comment was supposed to be making since some stringed instruments are clearly better than others and there is a lot of variability (especially when, as with table tennis blades, they are mostly made of wood). And of course, musical instruments don't produce pure sine waves, which is why a lute and a violin sound different even when they play the same note. |
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JRSDallas
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Edited by JRSDallas - 01/01/2015 at 8:22pm |
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Galaxy T1 89 gm
FH: HRT Huaruite Wujilong 2 - Dragon 2 II, Max, Black Donic Acuda S2, Max, Red |
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jrscatman
Premier Member Joined: 10/19/2008 Status: Offline Points: 4585 |
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It's very much an art rather than science.
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Butterfly MPS
FH: Donic Acuda S1 BH: Palio CK531A OX |
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Baal
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This is surprisingly true for blades too considering they are fairly mass produced. I have a bunch of Viscarias and two feel much h better than the others. Its not just weight. I guess that is what happens when you make things out of wood. |
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AgentHEX
Gold Member Joined: 12/14/2004 Location: Yo Mama Status: Offline Points: 1641 |
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> However, the problem I have here is that the OP title is - to me -
actually misleading. For I do not care that much about blade performance
(does anyone?) Rather, I care about racket performance.
The same aforementioned restitution ratio exists for rubber, except since the ball grips the surface the input parameters of spin and angle need to be characterized in addition to speed alone. > I have been watching lot videos about luthiers on youtube. They say every instrument they make is unique. A lot of what they do is by feel. With a musical instrument the notes required are standardized frequencies which human hearing can be well attuned to. |
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jrscatman
Premier Member Joined: 10/19/2008 Status: Offline Points: 4585 |
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I am also very interested in the feel of the blade, but don't know how to measure it or describe it. I have been watching lot videos about luthiers on youtube. They say every instrument they make is unique. A lot of what they do is by feel. One mentioned, he doesn't measure the thickness of the wood - he just feels for the correct stiffness - when gets there he stops.
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Butterfly MPS
FH: Donic Acuda S1 BH: Palio CK531A OX |
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pnachtwey
Platinum Member Joined: 03/09/2010 Location: Vancouver, WA Status: Offline Points: 2035 |
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This thread is interesting if you are going to make your own blades. Other than that most people will find a blade that feels good and play with it. If one puts identical rubbers on two similar blades they won't play that differently and there is no impulse ( trajectory ) that one paddle can generate than another can't. I don't feel there is much difference between my Samsonov Alpha with H3 Neo than my TBS with S2 on it. Yes they feel different but I can play the same way with both. People are very adaptable. I find the blade makes more of a difference when playing hard bat or with long pips 0X than with inverted because there is no sponge to mask the performance of the blade. |
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JacekGM
Platinum Member Joined: 02/17/2013 Location: USA Status: Offline Points: 2356 |
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This is a fantastic thread. Some people well familiar with Newtonian physics take on the aspect of how blade design will affect it's performance. Great, and thank you, and please continue...
However, the problem I have here is that the OP title is - to me - actually misleading. For I do not care that much about blade performance (does anyone?) Rather, I care about racket performance. Although the influence of the rubber sheet(s) has been, shyly, mentioned here and there above, there is this formidable component conveniently dropped from this discussion altogether: the quality and quantity of the glue layer(s). Oh, and the various types of handles, too, and also how the type of rubber on the other side affects the performance of a given racket side... Oh, boy... I do have a problem, I guess because I play with a racket and not with a blade... |
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(1) Juic SBA (Fl, 85 g) with Bluefire JP3 (red max) on FH and 0.6 mm DR N Desperado on BH; (2) Yinhe T7 (Fl, 87 g) with Bluefire M3 (red 2.0) on FH and 0.6 mm 755 on BH.
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AgentHEX
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It's worth taking another step back for a meta-discussion of this topic. The holy grail we're after is the ratio of the ball's speed coming off the blade divided by its speed going in for all such speeds. This can be done by a machine which controls for and measures ball speed, or equivalently by drop the ball from ever greater heights.
Since such a contraption is a pain to build, and meticulously dropping and measuring heights is also bit annoying (the ITTF does this for one height on the sanctioned balls against a hard platform, effectively placing a ceiling of ~.85 on the ratio above). Thus all these other numbers advanced are just somewhat more amenable proxies for this value. They're useful enough to indicate this blade is likely faster than that blade, but even in a more limited capacity they each have advantages and drawback. Personally I just look at the thickness with some adjustment for harder or softer plies (esp composite ones), and it's ~80% effective for <<20% of the work. As to playing differently, other than this speed metric it's just a subjective feel of what happens after the ball's left the blade. Some people for whatever reason don't like certain sounds or vibrations; for example I've been told ~ALL wood blades feel hollow, and a hard sponged Yinhe Moon I just tried on a Sweden Classic sounded broken/cracked etc. This has a significant internalized effect on confidence to swing for shots, etc; and because of that discomfort we're not likely to put in time to get used to a setup (compare this to folks expending considerable effort adjusting to pro setups obviously too fast for them, for similar psychological causes). Of course there's no social currency in presenting this as a largely subjective evaluation, so there's a tendency to attach "reasons" via peudo-technical terminology to support a personal bias. Blade X is good because of this and that nebulous aspect. As mentioned manufacturers are more than happy to play this game of attributing near-magical properties to a very easy to make piece of wood/fiber. |
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jrscatman
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But you must agree, each blade plays differently, how would you account for the difference? JRSDallas suggested frequency, is there some other property or properties we can use to measure blade performance?
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Butterfly MPS
FH: Donic Acuda S1 BH: Palio CK531A OX |
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AgentHEX
Gold Member Joined: 12/14/2004 Location: Yo Mama Status: Offline Points: 1641 |
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The thing is it's pretty easy to make a TT blade because the ball doesn't stick around for the vibration/resonance or other wood properties. It does change how you feel/perceive the equipment, but not so much the shot. It's understandable that's not what anyone least a community heavily invested in equipment wants to hear. But to be fair, I also have a rather large bag of TT blades and rubber (really they wouldn't all fit in any bag). |
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AgentHEX
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I think it's easier to learn a slower setup since it provides a larger range of physical motion to work with. A racket that doesn't allow the user to manipulate the ball as much least they miss tends to nudge players down a more tactical path. But this is still a sport where physical motion is more foundational given that better players can easily beat lesser ones with simply better shots, whereas the same can't be said for strategy as anyone who's ever been beaten by a kid with a proper loopdrive can attest to. That's why effective development programs mostly focus on getting the quality shots down first, and it's just easier for the less than athletically gifted (perfect timing, perfect swing control, etc) to do so with slow control equipment. |
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jrscatman
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This is quite interesting, so from a blade design point of view: what are the most important things a designer should focus on when building the ideal wood blade.
Also thought a short film interlude might help everyone to relax a bit: enjoy voilin wood resonance. ... Edited by jrscatman - 12/27/2014 at 6:26pm |
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Butterfly MPS
FH: Donic Acuda S1 BH: Palio CK531A OX |
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AgentHEX
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The long term effects of dampening (ie on vibrations) wouldn't affect the collision since the ball is well and off the blade as you're aware of. However the immediate dampening/inelastic effect of material, mostly the rubber and wood, would effect the energy lost during collision. That's why I mentioned thinking of this like a simulation rather than modeled equations, mostly to consider the details of what's actually going on during the relevant timeframe. In this case what's going on is the ball is largely the object doing the bouncing (deforming and rebounding with its own dampening), and everything else is better framed as a modifier to this behavior (in this case the dampening providing some "cushioning"). That's actually part of why these loosely affiliated indicators sort of work out: incidentally because nobody thought to change the main body of relevant factors. That and they're being used in the "slopey" part of COR, where any positive slope we're comparing against close enough to 1 has the appearance of sane results. ----- It's also worth stepping back and considering why these indicator happen to work. For frequency it appear for an object of given size, higher vibrational freq are correlated with lower energy loss. Something like elastic stiffness is similarly correlated with kinetic energy loss (of the ball here) in inelastic collisions. Note both of these are inverse correlations with the ball's collision COR. For visual thinkers, their inverse correlate to the loss, in a COR plot the space between that wolfram function and y=1. Edited by AgentHEX - 12/27/2014 at 5:58pm |
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AgentHEX
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Someone asked for a simple summary to help grasp what's going on. Please at least try to understand the easy explanation before criticizing the original arguments. The basic physics of beams and inertia have nothing specific do with composite constructions and applies to any and all physical matter. |
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pnachtwey
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Good one AgentHEX. I love it.
Obviously frequency isn't the only indicator. I have mentioned damping before but this topic always seems to be ignored. A few pages back you posted a series of wave equations but there was no damping term in those equations. If there were there would be a exp(-t/τ) where the tau in the denominator is the time constant of decay. Anything that vibrates has a damping factor or it would vibrate forever. In practical TT player terms, hands provide damping. A lose grip (more damping ) results in a slower return than a tight grip ( less damping). My Toxic 5 video shows the blade vibrating like crazy but it is in a vice. I doubt it would vibrate like that in my hand. Here is an example of what I am talking about http://ldf.mendelu.cz/und/sites/default/files/soubory_akustika/acoust_lect_damping.pdf There is more. Those that want to can find the rest of the document. Edited by pnachtwey - 12/27/2014 at 2:02pm |
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Krantz
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Calculating the distance from the center towards the face is crucial for measuring the stiffness of the blade and I am surprised that you seem to ignore this fact - properties of such composite constructions are being deeply studied in modern technology and manufacturing in things like rocket fuel tanks, super-light sport yachts and even cars bodies. If you mean that these calculations are wrong then please say exactly where the mistake is, because so far you are only presenting puzzles to readers and giving some homework to OP and personally I wouldn't even expect to get a serious answer for such nonconstructive critique. |
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