13.11.2015 Views

Dynamics cheat sheet

my dynamics notes - 12000.org

my dynamics notes - 12000.org

SHOW MORE
SHOW LESS

Create successful ePaper yourself

Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.

Similarly, µ 2 is found<br />

⎧ ⎫T ⎡ ⎤ ⎧ ⎫<br />

⎨ϕ 12 ⎬<br />

µ 2 = ⎣ m 11 m 12<br />

⎨ϕ ⎦ 12 ⎬<br />

⎩<br />

ϕ<br />

⎭<br />

22 m 21 m<br />

⎩<br />

22 ϕ<br />

⎭<br />

22<br />

{ } ⎡ ⎤ ⎧ ⎫<br />

= ϕ 12 ϕ ⎣ m 11 m 12<br />

⎨ϕ ⎦ 12 ⎬<br />

22<br />

m<br />

⎩<br />

22 ϕ<br />

⎭<br />

22<br />

m 21<br />

}<br />

=<br />

{ϕ ⎧ ⎫<br />

⎨ϕ 12 ⎬<br />

12 m 11 + ϕ 22 m 21 ϕ 12 m 12 + ϕ 22 m 22<br />

⎩<br />

ϕ<br />

⎭<br />

22<br />

= ϕ 12 (ϕ 12 m 11 + ϕ 22 m 21 ) + ϕ 22 (ϕ 12 m 12 + ϕ 22 m 22 )<br />

Now that µ 1 , µ 2 are obtained, the mass normalized shape vectors are found. They are called Φ 1 , Φ 2<br />

⎧ ⎫<br />

⎨ϕ 11 ⎬<br />

⎧ ⎫<br />

Φ 1 = ϕ ⎩<br />

ϕ<br />

⎭<br />

1 21<br />

⎨ √µ1<br />

ϕ 11 ⎬<br />

√ = √ =<br />

µ1 µ1 ⎩ √µ1<br />

ϕ 21 ⎭<br />

Similarly<br />

Φ 2 = ϕ 2<br />

√<br />

µ2<br />

=<br />

⎧<br />

⎨<br />

⎩<br />

ϕ 12<br />

ϕ 22<br />

⎫<br />

⎬<br />

⎭<br />

√<br />

µ2<br />

=<br />

⎧<br />

⎨<br />

õ2<br />

ϕ 12<br />

⎫<br />

⎬<br />

⎩ √µ2<br />

ϕ 22 ⎭<br />

1.5 Step 5, obtain the modal transformation matrix Φ<br />

The modal transformation matrix is the 2 × 2 matrix made of of Φ 1 , Φ 2 in each of its columns<br />

[Φ] = [Φ 1 Φ 2 ]<br />

⎡<br />

= ⎣<br />

⎤<br />

õ1<br />

ϕ 11 √µ2<br />

ϕ 12<br />

⎦<br />

õ1<br />

ϕ 21 √µ2<br />

ϕ 22<br />

Now the [Φ] is found, the transformation from the normal coordinates {x} to modal coordinates, which is<br />

called {η} is found<br />

{x} = [Φ] {η}<br />

⎧ ⎫ ⎡<br />

⎨x 1 (t) ⎬ ϕ 11<br />

⎩<br />

x 2 (t)<br />

⎭ = ⎣<br />

⎤<br />

õ1 õ2<br />

ϕ 12<br />

⎦<br />

õ1<br />

ϕ 21 √µ2<br />

ϕ 22<br />

⎧ ⎫<br />

⎨η 1 (t) ⎬<br />

⎩<br />

η 2 (t)<br />

⎭<br />

The transformation from modal coordinates back to normal coordinates is<br />

{η} = [Φ] −1 {x}<br />

⎧ ⎫ ⎡<br />

⎨η 1 (t) ⎬ ϕ 11<br />

⎩<br />

η 2 (t)<br />

⎭ = ⎣<br />

⎤<br />

õ1 õ2<br />

ϕ 12<br />

⎦<br />

õ1<br />

ϕ 21 √µ2<br />

ϕ 22<br />

−1 ⎧ ⎫<br />

⎨ x 1 (t) ⎬<br />

⎩<br />

x 2 (t)<br />

⎭<br />

7

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!