Motovated > News > Newsletter March 2008

Hello everyone,

Someone tells me it's Easter soon - does that mean that the first quarter of 2008 has already passed us by? This month's newsletter includes a quick case study, another brainteaser, some general tips for designing for contact and announces some upcoming FEA training. If you have any particular concerns or frustrations, email us and we will see if we can offer you a solution.

As always, if you have any projects that just aren't getting done, or you need a bit of advice, call us and we will be happy to help. Happy Easter everyone, we look forward to hearing from you soon.

Greg Morehouse
General Manager
Engineering Analyst

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Finite Element Analysis Training

Motovated will be providing a series of training sessions focussing on modern, easy-to-use FEA packages, starting with what these tools can do for your business, then showing you how to use them in the real world. The dates and topics of each session are as follows:

15th April (am) - Introduction to Easy-to-Use FEA - This session will be a generic introduction into the principles of FEA, highlighting what it can do for you and what its limitations are.  Suitable for new users as well as managers requiring sufficient understanding to know if the process is right for their organisation.

15th April (pm) - Introduction to COSMOS DesignSTAR & COSMOSWorks - This hands-on session will highlight the ease of use of the new generation of FE software, including its associativity to native CAD data including Solid Edge, SolidWorks, Inventor and ProE.

16th April (am) - Real World FE Modelling - This hands-on session will highlight the challenges faced with some very common FE problems, and some cunning solutions developed to work around some of the limitations of the new generation of easy-to-use FE software.

16th April (pm) - Analysing Your Products - This hands-on session will allow you to bring along your solids and problems, allowing you to work out how you would analyse some of your own challenging issues.

Each session will be held in Christchurch, and you can attend individual sessions if you wish. For more information visit: http://www.motovated.co.nz/news/mar08. If you would be interested in similar training sessions at different times or locations, please get in touch.

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Case Study: Seafury SF18 Surface Piercing Drive Unit

Motovated Design & Analysis recently helped Seafury International Ltd bring a new surface piercing outdrive product line to market.

Seafury produce a range of surface piercing drives and propellers for the marine industry. These units have the top half of the propeller exposed during planing, compared to conventional installations where the entire propeller is submerged. As a result, the propeller and rudder carry significant bending and torsional loads. The advantages of this set up are, however, reduced drag forces, greater efficiencies and higher planing speeds.

Motovated carried out a range of stress and frequency analyses to check component strengths at 48 knots (90 kph), and accommodate future upsizing to 70 knots.

The first step was the development of appropriate rudder loads from test data requested after previous analyses. An analysis of the surface drive assembly was then undertaken, including a portion of the transom to check the transom flange bolt loads.

The rudder design was initially a stainless steel weldment of the rudder stock and blade. As a result of the stress analysis several changes were made, including casting the part in Aluminium Bronze to minimise fatigue issues. The analysis also highlighted several areas of stress concentration which were easily relieved by tweaking radii and section transitions.

To read this case study in full, and for more information on the Seafury surface piercing drive units, visit our website at: http://www.motovated.co.nz/casestudies/seafury.html

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Outsmart your colleagues!

Did you get our January Newsletter's question right?

A blacksmith is given five pieces of chain, with three links in each chain. He has to connect the pieces together to make a single chain. How many links does he have to open and then close again to do so with the least amount of effort?

The answer was of course 3 rings – by opening one set of 3, you are able to join the other 4 sets together. Congratulations to Andrew Ireland of Infact Ltd, a Mitre 10 voucher is on its way to you. An honourable mention to Johannes De Beer in Australia for providing the diagram above showing the solution. Click on the image for a larger version.

And now for this issue's question:

John walks over a railway bridge. When he is just ten meters away from the middle of the bridge, he hears a train coming from behind. At that moment, the train, which travels at a speed of 90 km/h, is exactly as far away from the bridge as the bridge measures in length. Without hesitation, John rushes straight towards the train to get off the bridge and misses the train by just four meters! If John would, however, have rushed exactly as fast in the other direction, the train would have hit him eight meters before the end of the bridge.

What is the length of the railway-bridge?

Send your answer to chris@motovated.co.nz to be in with a chance of winning a $50 Mitre 10 voucher.

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Tips & Tricks: Designing for Hertzian Contact

Sometimes in machine design it is very difficult to avoid line or point contact with fairly high loads. Rather than redesign your machine to avoid this situation, a bit of analysis can go a long way to deciding whether this is a problem, and if there are some easy things that can be done to reduce or eliminate spalling.

If one or more of the contact surfaces is curved, such as in the hook example below, the fairly simple Hertzian contact formula can be used to calculate the contact half-width:

The area of these contact patches can be larger than you'd expect, and can be capable of transferring high loads, especially if you can select materials with low Young's modulii or Poisson's ratios.

Sharp edge contact should be avoided, but adding a simple round to the edge will reduce the contact stress and allow this equation to be used.

[Equation from Shigley. J.E "Mechanical Engineering Design"]

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Enjoy the Easter break. We look forward to continuing to provide you with the best engineering services and advice possible.

Greg and the team at Motovated.