DX Upper Tree-House & Fan

12 June, 2010Esguerra

Definition• “Blue sky” recommendations assume

– Sufficient budget– Sufficient schedule– Sufficient manpower

Access from this side.

M3 swing-arm

•Upper DX tree-house structure• Rigidly attached to C-ring extension• Upper fan enclosure also rigidly attached to C-ring extension

•Upper DX tree-house structure• Attached to C-ring extension• Upper fan enclosure also attached to C-ring extension• All rigid attachments

Comments• It makes sense to isolate the C-ring extensions from any source of

vibration• The tree-house and tree-house ventilation are vibration sources

– As demonstrated through AO testing– As demonstrated through vibration testing

• “Blue-sky” recommendation– Replace all rigid attachments to the C-ring extension with isolation

• Wire-rope isolator?• Elastomeric?• Flexure?

– Isolation performance should be *tested*• Quantitative test of isolation under representative loading• Testing before and after installation

– To verify improvement– To quantify performance

DX Upper Tree-House Fan

DX Upper Tree-House Fan Motor

• Operating at current low speed (16-Hz), there is obvious undesirable motion of the motor

• Motor is mounted through elastomeric pads to sheet-metal– The sheet-metal base is probably as compliant as the isolators for small displacements

• Whole motor assembly wobbles– Compliance of the sheet-metal structure– Varying belt tension during operation– Motor imbalance / cogging?

• Belt might also have dynamics– At higher speeds

• Balancing the fan will not fix any of this

Tensile Load

Motor rocking motion(coning)

Rubber mounting pads

DX Upper Tree-House Fan

• Fan is a “squirrel cage” type• Connected to motor by belt/pulley (1:1)• Bearing and pulley attached to sheet-metal

through flimsy looking assembly

Tensile Load

I would guess that this is not very stiff.

“Blue-Sky” Recommendations

• Eliminate pulley system– Direct drive, or through viscous damper, or bellows– Use a different fan/motor

• Attach fan and motor to common “frame”– Frame should be stiff– First mode (of assembly) should be higher than motor disturbance

• Should be able to measure motor disturbance frequencies directly• <1-second decay; (8% damping@10-Hz, decreasing OK with higher frequencies)

• Isolate common fan/motor frame– Isolate fan/motor connection to tree-house

• Isolation first mode should be less than lowest motor/fan disturbance frequency• Damping is good (don’t use normal springs)• Wire rope isolation?• Flexible ductwork from tree-house to fan assembly/heat exchanger compartment

– Isolate connection to C-ring extension if connection is necessary• Balance fan/motor before reinstallation

– Recommend testing in-lab before installation• If there is still appreciable vibration

– Additional passive or active vibration attenuation at the fan/motor frame– TMD or active vibration control

“Blue-Sky” Recommendations

• Isolation performance should be *tested*– Quantitative test of isolation under representative loading– Testing before and after installation

• To verify improvement• To quantify performance