Vibratory System

Discussion in 'Hydrodynamics and Aerodynamics' started by gonzo, Jul 25, 2018.

  1. gonzo
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    gonzo Senior Member

    That drawing is not a free body diagram. I don't know what you mean by a "conceptual sketch" though. If there is only one force input and there is not opposite and equal reaction, then it is outside of Newtonian physics and, as far as we know, does not exist in this Universe. If you leave the reaction forces out, the drawing is not a free body diagram. Also, free body diagrams can not be cancelled; they are a representation of the basic force vectors. A horizontal force can not have a vertical reaction force.
    Also, you previously stated that a nylon rode stretching is a shock absorber, not a damper. A damper is an element that dissipates energy. A shock absorber is a damper.
     
  2. gonzo
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    gonzo Senior Member

     
  3. MikeJohns
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    MikeJohns Senior Member

    Gonzo
    Isn't that what I just said? You were the one calling it an incorrect drawing of a free body diagram !
    But it's not meant to be a free body diagram. It shows the relative movement of the components.

    So go ahead sketch the free body diagram and see which forces cancel out ( equal and opposite) Make sure you include the tension vector.

    And can you state where you think the force comes from to do the work of lifting the chain?
     
    Last edited: Aug 7, 2018
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  4. gonzo
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    gonzo Senior Member

    I already stated several times where the vertical component comes from. However, be careful about mixing force with work. The latter is a function of time. The buoyancy of the hull and the pitching moment are the upward vertical force. The downward vertical force are caused by the weight of the chain, the weight and hold force of the anchor (if all the chain is lifted ). A diagram with relative movement of components is not relevant to the discussion. A free body diagram is. Since you are claiming a horizontal force can create a vertical reaction force, please explain what you mean with a free body diagram. It only involves four forces at the join between the rode and the boat.
    What do you mean by "tension vector", and why would you not stay withing the x-y orientation as the rest of the forces?
    You are making a claim that goes against all recorded facts in physics. A simple FBD would be an easy way to show how that works.
     
  5. MikeJohns
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    MikeJohns Senior Member

    Just force times distance for work. You are getting confused with energy ( I have said that you need to understand the difference between force work and energy).

    So looking at Ray Watsons diagram of movement of the components, where does the force actually come from that does the work of lifting the chain? All you are considering is buoyancy opposing m.g in the vertical plane in the steady state after the wind force is introduced.

    But a force did some work , the only force inputing energy into the system is horizontal. The force doing work to lift the chain has to be a vector component of the horizontal force, it doesn't originate from buoyancy.

    Here's a better sketch I just drew. The tension vector is the inline force in the cable, it's different at either end, at the lower end T is equivalent to the anchor holding force. Gonzo forces.jpg
    [​IMG]
     
    Last edited: Aug 7, 2018
  6. Ad Hoc
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    Ad Hoc Naval Architect

    Good god....now you're saying a piece of sTring...with a T...is a sPring with a P.

    So, please show me stiffness constant for a piece string...and then explain how this piece of string with a newly found stiffness constant can provide a restoring force when it is extended by a distance 'x'.

    And while you're at it....you still have not drawn the free body diagram of the balloon...c'mon. Please!....put everyone out of their misery.
     
    Last edited: Aug 7, 2018
  7. gonzo
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    gonzo Senior Member

    You just quoted the value of K for the string. Take time to read it before have a knee-jerk reaction.
     
  8. gonzo
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    gonzo Senior Member

    The vertical component at the bow is less than mg. There is a vertical component at the other end of the rode too.
    It is also incorrect to mix forces, energy and work in a FBD. The correct way to draw a FBD is to separate each element and indicate the forces, velocity and acceleration for each.
    The force to lift the chain is from buoyancy. A FBD is the system at a point in time (= 0), so there is no work done since no time passed.
     
  9. TANSL
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    TANSL Senior Member

    Nothing happens in the world if time does not pass.
    That is very true, for example, the more time goes by, the more work humanity does and the non-human elements, as a force for example, can not do any work if time does not pass. In that we must recognize that Gonzo is right. Looking at it, from another perspective, without time, we are nothing, we do not have time to be anything
     
    Last edited: Aug 7, 2018
  10. Ad Hoc
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    Ad Hoc Naval Architect

    Sorry, no I didn't.
    I am asking YOU for the stiffness constant of string, as you are claiming sTring is a sPring.

    And then you can show me how good string is as a spring, and show me some good examples of high quality sPrings made of sTring i can replace on my car during its next service, because the existing ones are not good enough.
    Since sTring it is a well known sPring.

    Then you can show the free body diagram of the balloon as constantly requested yet constantly ignored.
    C'mon any qualified engineer could do this in their sleep.
     
  11. MikeJohns
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    MikeJohns Senior Member

    I think you've been spending too much time with your spiritual guide :)
     
  12. TANSL
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    TANSL Senior Member

    Mike, not only talking about physics can one say nonsense and, since this thread is already somewhat devalued, let me also say nonsense with philosophical airs.
    The statement "Nothing happens in the world if time does not pass" is overwhelming
     
  13. MikeJohns
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    MikeJohns Senior Member

    I’ve added the at rest vessel that we are exciting with a step function for illustration.

    Presuming the catenary seabed touchdown is before the anchor.

    There are only forces in the diagram I’ve drawn, (a tension vector is a force).

    You can see that the upward seabed reaction at the anchor doesn’t have any input. Similarly buoyancy is just another reaction not an input.

    You can model the ideal sytstem from the forces shown in this diagram. It’s pretty fundamental.

    What force does the WORK of lifting the chain between the two equilibrium states? Its found by resolving the tension vector. The tension vector is in turn a function of the catenary.
    But there's only one input to the system, surely you can see that ?


    For Gonzo 2.jpg

    [​IMG]
     
    Last edited: Aug 7, 2018
  14. MikeJohns
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    MikeJohns Senior Member

    Looking over your posts I see I missed addressing this:

    Look up the definition of JERK .

    You'd probably better type in "the physics expression Jerk"

    I did try and explain this earlier from energy principles but you just contradicted refusing to accept the terms Gravitational and Strain energy.

    The shock absorber Reduces the rate of change of acceleration. (aka Jerk)
    The damper Disperses energy from the system in such a way that it has no future effect.
     

  15. gonzo
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    gonzo Senior Member

    I don't see how you can treat an anchoring system as a step function. That means that is has only two states, which we know it not true.
     
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