ES Journal - 2019/2020

theapprentice · Mar 3, 2020

theapprentice said:
SS 3077
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out 3053 +24

themickey · Mar 3, 2020

vanzandt said:
5.3.2 Using Free Vibrations to Measure Properties of a System

We will describe one very important application of the results developed in the preceding section.

It often happens that we need to measure the dynamical properties of an engineering system. For example, we might want to measure the natural frequency and damping coefficient for a structure after it has been built, to make sure that design predictions were correct, and to use in future models of the system.

You can use the free vibration response to do this, as follows. First, you instrument your design by attaching accelerometers to appropriate points. You then use an impulse hammer to excite a particular mode of vibration, as discussed in Section 5.1.3. You use your accelerometer readings to determine the displacement at the point where the structure was excited: the results will be a graph similar to the one shown below.

We then identify a nice looking peak, and call the time there , as shown.

The following quantities are then measured from the graph:

1. The period of oscillation. The period of oscillation was defined in Section 5.1.2: it is the time between two peaks, as shown. Since the signal is (supposedly) periodic, it is often best to estimate T as follows

where is the time at which the nth peak occurs, as shown in the picture.
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Interesting, but I think of humans as creatures which swarm rather than a type tuning fork mechanical object.

theapprentice · Mar 3, 2020

halfway point at about 2996 for a long if it gets there?

theapprentice · Mar 3, 2020

theapprentice said:
Half Way point at 3081 ish
might try short there
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worked out nice

themickey · Mar 3, 2020

Specterx said:
Yeah, pretty funny. I thought they were deliberately holding fire out of basic common sense - financial conditions aren't within a thousand miles of an actual crisis point, and there's no point whatsoever to cutting rates multiple weeks or even months before covid hits its peak. Better to wait until the virus situation stabilizes before taking action, rather than panic now and see the production shutdowns, market selloff etc. anyway. I guess Trump got his way?

Caveman Powell caves again!
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I'm suspecting an ulterior motive.
I'm suspecting that for quite some time now they deliberately wish to drive down rates, has nothing to do with the economy and COVID-19 is just one perfect excuse to implement this faster.
Australia lowered rates today as well, just at the drop of a hat, imo it's a concerted effort by Western gummints working together.

Mo06 · Mar 3, 2020

Be nice to see the SPX with an 2 in front....

Mo06 · Mar 3, 2020

Maybe getting there.

Laissez Faire · Mar 3, 2020

Interesting development.

4 % down at 2965.

Looks like another record range in the making.

theapprentice · Mar 3, 2020

theapprentice said:
halfway point at about 2996 for a long if it gets there?
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Wow. Got there fast. Dropped like 35 points to get there from my post 30 mins ago lol

Long 2996

Mo06 · Mar 3, 2020

Suspect we will retest the lows before Friday...