… brought to you via Smurf on Spreadsheets
If you want your spreadsheets to go faster, Charles Williams is the man to tell you how to do it. Charles has recently started a blog on the subject: FastExcel
Well worth a quick look.
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Jaqui Mcshee
Usually when I’m searching YouTube to see what new old stuff has come up I type in Jansch or Renbourn or Thompson, but today just for a change I typed Mcshee, and this is what came up:
which lead to:
and:
Dynamically Defined Dancing Pendulums
Following the previous post, I have re-created the animation using a non-linear dynamic analysis inside Strand7, rather than by feeding in the positions of each ball at each time step. The input using this approach is much simpler; just set each pendulum with an equal angular off-set, and specify the direction of gravity, and then let the program work out where they go. The first animation generated with this approach was visually nearly identical to the version generated with specified coordinates, which was encouraging, but didn’t make for a very interesting video. To add a bit of variety, and to replicate the behaviour of real pendulums more closely, I have also added some “viscous damping”, which gradually reduces the amplitude of each pendulums movement:
Details of the Strand7 animations settings:
- Analysis Type: Nonlinear transient dynamic analysis
- Non-linear options: Nonlinear geometry selected (nonlinear materials and creep not required)
- Time steps: 18,000 steps at 0.005 sec increments, save every 10 steps.
- Viscous damping selected
- Pendulum strings defined as steel wire with a diameter of 2 mm
- Pendulum viscosity set at 25 kN.s/m/m^3 (set by trial and error to reduce amplitude by about half over 90 seconds)
- Iteration limit = 20, Displacement Norm Tolerance = 1e-6, Residuals Norm Tolerance = 1e-5
First attempts had problems with the analysis becoming unstable after a few seconds, which were resolved by:
- Reducing the time step
- Reducing the displacement and residuals norms
- Reducing the stiffness of the pendulum cables
Posted in Finite Element Analysis, Newton
Tagged dynamic analysis, Pendulum animation, Strand7
2 Comments
Dancing Pendulums
This animation was produced in response to a video of real pendulums performing similar tricks:
Not having an animation program I thought I’d use the finite element program Strand7. Modelling the pendulums was easy, just 15 beam elements with a “translational mass” attribute on the end (more on the exact length of each pendulum later).
Strand7 Pendulum Model
Strand7 will perform a dynamic analysis, so I could have given each pendulum a displacement and then carried out the analysis of their movements over 90 seconds, but because I was only interested in generating the patterns in this case I decided to take the easy way out and generate the pendulum movement by inputting the displacements directly. The procedure was:
- Set up 30 “freedom cases”, each with the lower end of a different pendulum given a unit deflection in the X or Y direction
- Set up a series of 1800 increments, corresponding to time steps of 1/20 second, and factor each freedom case to replicate the pendulum motions.
- Run the analysis
- Create an animation of the resulting pendulum motions, using an end on view as in the original video
The only remaining problem was how to enter 1800 x 30 factors quickly and accurately. The solution (naturally) was to set up a table of the X and Y displacements of each pendulum in Excel:
Freedom case factor table
These factors were then transferred into Strand7 using the program’s API (the use of which I will describe in more detail in later posts).
The only remaining detail was to find the correct pendulum lengths to generate the patterns I was after. After a little experimentation it became clear that each pendulum much have a different integer number of cycles over some fixed period. I fixed the first pendulum length at 350 mm, which has a period of 1.187 seconds, or 51 cycles over 60.558 seconds. The other pendulum lengths were then adjusted to have 52 to 65 cycles over the same time period, giving a range from 336.7 mm to 215.5 mm.
Posted in Animation, Excel, Finite Element Analysis, Newton
Tagged animation, API, Pendulum patterns, Strand7
5 Comments
Android apps
Following yesterday’s post about my new toy, this one is about some of the applications to make it go. It will be fairly brief because I haven’t had a lot of time to explore, but the main aim is to provide a space for reader’s comments, so if you have an Android app you like, please leave a comment and let us know about it.
Office Stuff
- “Docs to Go” reads MS Office documents and pdf files. I upgraded to the “pro” version for about $14, which allows editing, jump to a page number in a pdf file, see more than the first sheet of a spreadsheet and various other enhancements. I’m happy with the pdf reader, but the Office readers are disappointing. Word files are wrapped to fill the screen for any zoom level, and many graphics appeared as black boxes. In Excel the text is displayed reasonably well, but it seems it doesn’t display charts at all.
- E-cell xls Pro: Display also disappointing with no charts, and the text formatting shown much less accurately than Docs to Go. Editing text does seem easier though. Both Excel programs offer no VBA support.
Other stuff:
- Gallery – the built-in image file viewer, works very nicely, fast and good resolution with a very intuitive interface.
- Barcode scanner – scans all sorts of barcodes, worth the free download if only to scan bar-code links to other applications.
- Cam scanner – scanned documents from camera images. Didn’t work well on the one I tried, but maybe the Acer camera just isn’t up to it. I’ll try it with some images from my SLR some time.
- Convert pad – nice unit conversion program. Very easy to use and fairly comprehensive. I just wish I could copy and paste into Excel easily.
- Autocad WS – this is very nice, you can upload Autocad drawings and view and edit them, all from your browser. Just requires a free account set up.
That’s all for now. Anyone with a good Android app, please leave a comment.
