## Thursday, October 30, 2008

### 5Bicycle Structural Dynamics by VélUS

Mechanical Engineering researchers Y. Champoux, S. Richard and J. Drouet from the University of Sherbrooke (Canada) aim to help bicycle manufacturers study the dynamic behavior of bicycles so they can understand the real implications of their design in actual riding conditions.

The trio belong to the VélUS bicycle research team, and I had introduced them to you a couple of months back through a post on estimating bicycle fatigue. (See HotSpot Method For Bicycle Fatigue Life).

Presented below is a paper they did on structural dynamics and it had appeared in the Sound and Vibration Control Magazine. The components and the frame of a bicycle are subjected to time-varying force excitations imposed by the cyclist and by the road. Its dynamic behavior becomes an important issue, because it is directly linked to the bike lifetime, maneuverability, efficiency and comfort. The researchers describe the bicycle structure in terms of its natural characteristics which are the frequency, damping and mode shapes - its dynamic properties.

Preliminary Resources You May Find Helpful :

Size, Rattle and Modal Analysis - An article in the Machine Design magazine

Experimental Modal Analysis : A simple non-mathematical introduction

Modal analysis explained in simple terms

Basic steps involved in experimental modal analysis

Modal analysis - Mathematical introduction

Vibration and Waves

Machine Vibration Basics

Introduction To Statics And Dynamics (An Excellent Online Book From Cornell University)

Damping Ratio

Transfer Functions

Strain Gages : Back to Basics

How Accelerometers Work

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1. Anonymous8:44 PM

Iread the conclusion and it had more to do with engendering a relationship between Universities and Industry. Can you abstract for us what was learned about bicycles?

2. Anon : Apologies for taking things for granted here. Again, even I'm not an expert in modal analysis. I have posted some additional resources that could help everyone. This stuff is like the bread and butter in structural circles and is used in the civil, automotive and aeronautical fields.

A mode of vibration is a characteristic pattern or shape in which a mechanical system will vibrate. Most systems have many modes of vibration, and it is the task of modal analysis to determine these mode shapes. The actual vibration of a structure is always a combination or mixture of all the vibration modes. But they need not all be excited to the same degree. For instance, if a bell is rung softly, we hear primarily the fundamental mode of vibration, but if it is hit harder, other modes are excited, and we hear the upper partials of the tone.

Same thing here with the bicycle. What VelUS is trying to do is to appreciate the bicycle as a dynamic, vibrating system with a rider that influences it more. Where vibrations are involved, the challenge lies in better understanding its dynamic properties using analytical, numerical or experimental techniques.

I feel its a great thing that literature like this is coming out. Weight and stiffness issues are not only the concern with bikes, vibration and fatigue is too. A lot of the knowledge behind vibration, dynamics and fatigue properties on bicycles lie steeped in mystery and folklore. At other times, its concentrated in journals and papers and within scientific circles. Its time that these groups start collaborating more with manufacturers so we can have better designed bikes that are safe and most importantly, comfortable to use. Why not?!

3. Anon : If you'd like to see a visual of vibration modes in a simple tuning fork, I have a video for you. Check it out for some more understanding of the issue at hand.

4. Anonymous12:19 AM

Hi

FEA modal analysis was used in designing the AIS/RMIT Australian track bike (superbike)

Article can be found here http://www.powerhousemuseum.com/hsc/bike/article.htm

5. ...it's interesting, in a way...

...these gentlemen have designed a highly complex electronic & mechanical system to measure, record & analyze primary, secondary & extraneous frequencies throughout the entire structure of first a bicycle itself & then a bicycle w/ a rider...the intent being to improve upon the riding qualities you mentioned, ron...maneuverability, efficiency & comfort within the context of the fatigue rate of the frameset...

...in essence, they are deriving & analyzing more information about the bicycle than has ever been understood or utilized up to this point in time...

...now...without condemning or denigrating their work, because i do find it fascinating, i also find it to be intriguing that the bicycle only ever slowly evolves & improves as a machine...

...in other words, nothing groundbreaking really happens at any one time, in the engineered form of the bicycle...it is a constant evolutionary process...

...which makes a strong statement about the early collective genius that created the basic safety bicycle...

...ultimately, the results that they come up w/ may prove to be worthwhile for we the consumer / enthusiast...

...what i find interesting is the trade off regarding money & time in relation to actual valuable information gained...

...will it prove to be worthwhile in the long run ???...only time & riding will tell...

Thank you. I read every single comment.