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  1. J

    CFD analysis of a starfish?

    Even if you are only interested in a comparison between two competing designs, I strongly recommend you to go for a full scale test, specially because it is possible to do. This will give much more substance to your research and will probably save you time and criticism.
  2. J

    Fatigue analysis:frequency domain vs time domain

    I might have, what are you looking for?
  3. J

    Educated opinions please: Are seats in rear crumple zones unsafe?

    I understand, but by working with the wrong units, the calculated force is 1 order of magnitude higher. By the way, even calculating with the wrong units, the answer should be 2x10^7 N instead of 2x10^8 N, which leads to a total error of two orders of magnitude higher. I see that you are...
  4. J

    Educated opinions please: Are seats in rear crumple zones unsafe?

    I am not sure about what you are trying to calculate, but the velocity term should be in [m/s] instead of [km/s] or [kph] to keep units consistent.
  5. J

    FredGarvin - Question For You Please

    The book is "Roark's Formulas for Stress and Strain" and the equation comes from Table 14-1, chapter 14, p.702 (7th edition, 2002). For background information, look for hertzian stress or contact stress.
  6. J

    Fatigue analysis:frequency domain vs time domain

    I will try to clarify based on DNV standard OS-F201 Dynamic Risers (http://exchange.dnv.com/publishing/Codes/download.asp?url=2010-10/os-f201.pdf" [Broken]). In fact, there are no explicit requirements to design based solely on a time domain analysis, but there are three interesting tables on...
  7. J

    Fatigue analysis:frequency domain vs time domain

    I did not state that, what I am saying is: "Often, frequency domain analysis cannot be replaced by a time-domain analysis". You are very right here, except that you are implying that by linearizing you are inevitably\permanently losing the analysis accuracy, which is not always true...
  8. J

    Fatigue analysis:frequency domain vs time domain

    The decision whether to go for a frequency domain analysis or a time domain analysis is not straightforward, and there are some main factors you should account for. I will try to summarise, but beware they will not be enough to assure anyone that the "best" approach will be attained. Often...
  9. J

    Uranus and Neptune Orbiters

    As you stated, Neptune and Uranus are unarguably invaluable to science for several reasons and the community knows it, but have been left out of probe missions due to current propulsion technology limits and budget. There are future missions planned to be launched around 2020 and beyond, but...
  10. J

    Help with plot for mystery

    Given the right conditions, this "jetstream" from a blowout, have a greater probability of sinking the overpassing boat, due to a sudden loss of buoyancy caused by the water vapor and the mixed expanding gases reaching the surface, rather than actually sand blasting the hull.
  11. J

    Project help

    The homepage is now available at: http://hovercrafthomepage.blogspot.com/p/hovercraft-design-calculator.html
  12. J

    Why the moon looks bigger at the horizon

    I reviewed PhanthomJay posts, and I think you are right.
  13. J

    Why the moon looks bigger at the horizon

    On the Southern Hemisphere, the Harvest Moon was on March. How could you see the moon larger on the Northern Hemisphere, on August, while it had a normal size for viewers on the South, and vice-versa on March ...
  14. J

    Flying wing aircraft.

    Not exactly, load the second video and seek to 01:44, look carefully at the glider, what do you see ? Please, continue reading this post after you did that. In the first video you can see the delta gliders soaring, and feel their instability under low speed, which is expected. Danger might add...
  15. J

    Blow Out Preventers

    russ_watters is right. The BOP knives must have the force to cut through the drilling column. Any accidental closing is always undesirable, because going back to drilling means running lengthy systems and equipments checkups and also one would have to face the problem of trying to fish the...
  16. J

    Contact Stress - Can we add it up?

    Also, look for Hertzian Stress, Tribology and Wear to get a better view about this interesting subject. What is the required factor of safety for the contact stress you found? Usually, the allowable stress is 4 for linear contact and 5.5 for point contact, but this varies a lot depending...
  17. J

    A plan for the private colonization of the moon

    I think you should move on to cost estimates. Next, what do you think about outlining your enterprise with the help of PMBOK ?
  18. J

    Flying wing aircraft.

    Ops, sorry about the ride.
  19. J

    Flying wing aircraft.

    These are RC hand launched gliders:
  20. J

    Pressure Vessel End Cap Velocity

    Hydrostatic pressure limits the amount of kinetic energy transferred to the end-cap, as the water will not push the end-cap further after the breach, instead, the water will drop and flow to the ground. If the flow rate is too high, the water flow will become as hazardous as the end-cap...
  21. J

    Plate deflection theory vs FEA: same problem, same parameters, different results

    You're welcome. For this to work, you cannot restrain more than one degree of freedom. A simply supported boundary condition will restrain only the vertical direction.
  22. J

    Choose a design based on stress

    Can you explain which design offers more strength ?
  23. J

    Choose a design based on stress

    If your only criteria is yield stress, not deflection, neither fatigue life, nor weight or cost and not manufacturing. Then you are solely talking about Factor of Safety. In that case, design two will handle more accidental loads than design one, under the same requirements.
  24. J

    Caspian Sea Monster vs Conventional Airlift

    The original Titanic was about 883ft long and DWT 46,328t. Today, the largest in service ship, in length, is the containership Emma Maersk with 1302ft and DWT 156,907t. But the record is held by the tanker Seawise Giant with 1504ft and DWT 564,763t, unfortunately already scrapped.
  25. J

    Force in a static member

    Draw a free body diagram for the tip of the beam, decomposing W and check where is theta.
  26. J

    Plate deflection theory vs FEA: same problem, same parameters, different results

    No, it is different. Clamped-Clamped will restrain the rotations also, therefore reducing the maximum deflection. *Re-run as simply supported.
  27. J

    Trying to figure out the density of water?

    Try this chart, you might find a better one elsewhere: http://www.engineeringtoolbox.com/fluid-density-temperature-pressure-d_309.html To solve the problem: What is the water density and, therefore, the water mass ? Can you now tell the combined mass ? What do you have to know to estimate the...
  28. J

    Plate deflection theory vs FEA: same problem, same parameters, different results

    I tried http://www.efunda.com/formulae/solid_mechanics/plates/calculators/SSSS_PUniform.cfm#Results and got 53.3nm for mxn=32x32 which agrees with your result. I solved the problem with CosmosWorks shell elements and got 53.35nm. Are you working with shell or solid elements ? I tried with...
  29. J

    Designing Moon Buggy frame need help

    According to the rules, flywheels are not allowed. If you implement a propeller, it will act as a flywheel also, even with a very low energy storage capacity and your design might not be allowed in the competition. Also, the power source is the same both for the wheels and the propeller...
  30. J

    Name of asteroid that'll pass very close

    http://neo.jpl.nasa.gov/
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