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Eduardo Kausel-Fundamental solutions in elastodynamics_ a compendium-Cambridge University Press (2006)

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10.3 Stiffness matrix method <strong>in</strong> cyl<strong>in</strong>drical coord<strong>in</strong>ates 171<br />

Torsional po<strong>in</strong>t source (n = 0)<br />

A torsional po<strong>in</strong>t source of unit <strong>in</strong>tensity can be obta<strong>in</strong>ed as the limit of a tangential r<strong>in</strong>g<br />

load p θ act<strong>in</strong>g on a r<strong>in</strong>g of radius r 1 → 0, which elicits a torsional moment M t = 2π ˜p θ r 1 = 1<br />

(observe that ˜p θ is the traction per radian, so the total r<strong>in</strong>g load is 2π times larger, and<br />

multiplication by the radius gives the moment). Hence, the load vector <strong>in</strong> the frequency–<br />

axial-wavenumber doma<strong>in</strong> for a torsional po<strong>in</strong>t source of unit <strong>in</strong>tensity is<br />

⎧ ⎫ ⎧ ⎫<br />

⎨ ˜p r ⎬<br />

p 1 = ˜p<br />

⎩ θ<br />

⎭ = 1 ⎨ 0 ⎬<br />

1<br />

(10.125)<br />

2πr<br />

−i ˜p 1 ⎩ ⎭<br />

z 0<br />

Hence,<br />

⎧<br />

( ) 1<br />

π<br />

⎪⎨<br />

lim<br />

r1→0 (r1F11)−1 p 1 =<br />

( ( ) ) 2 2πr1<br />

4µ 1 +<br />

kz<br />

kβ<br />

⎪⎩<br />

that is,<br />

− kα<br />

kβ<br />

( ( ) ) 2<br />

1 −<br />

kz<br />

⎫<br />

zβ 0 −2 kα kz<br />

kβ<br />

kβ kβ<br />

( ( ) )<br />

⎫⎪ ⎬<br />

⎧⎪ ⎨ 0 ⎪⎬<br />

2<br />

0 − 1 +<br />

kz<br />

zβ 0 1<br />

kβ<br />

⎪<br />

−2 kz zβ 0 2 ⎪ ⎩ ⎭ 0<br />

⎪⎭<br />

kβ<br />

(10.126)<br />

⎧ ⎫<br />

lim (r 1F 11) −1 p 1 = k ⎨ 0 ⎬<br />

β<br />

1<br />

r1→0 8µ ⎩ ⎭ (use to form p 2eq) (10.127)<br />

0<br />

Axial po<strong>in</strong>t load (n = 0)<br />

This load can be visualized as the limit of an axial r<strong>in</strong>g traction per radian, p z , act<strong>in</strong>g on a<br />

r<strong>in</strong>g of radius r 1 → 0, which implies an axial load P z = 2π ˜p z = 1. Hence, the load vector<br />

<strong>in</strong> the frequency–axial-wavenumber doma<strong>in</strong> for a unit axial load is<br />

⎧ ⎫ ⎧ ⎫<br />

⎨ ˜p r ⎬<br />

p 1 = ˜p<br />

⎩ θ<br />

⎭ = −i ⎨ 0 ⎬<br />

0<br />

(10.128)<br />

2π ⎩ ⎭<br />

−i ˜p z 1<br />

lim (r 1F 11) −1 p 1 =<br />

r1→0<br />

( ) −i<br />

2π<br />

⎧<br />

⎪⎨<br />

×<br />

⎪⎩<br />

− kα<br />

kβ<br />

(<br />

4µ<br />

π<br />

( ) ) 2<br />

1 +<br />

kz<br />

kβ<br />

( ( ) ) 2<br />

1 −<br />

kz<br />

z<br />

kβ β 0 −2 kα<br />

kβ<br />

( ( ) ) 2<br />

0 − 1 +<br />

kz<br />

z β 0<br />

−2 kz<br />

kβ z β 0 2<br />

kβ<br />

kz<br />

kβ<br />

⎫<br />

⎧ ⎫<br />

⎪⎬ ⎨ 0 ⎬<br />

0<br />

⎩ ⎭<br />

1 ⎪⎭<br />

(10.129)

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