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Blade transmissibility by FEA

Justin Greenhalgh,

Rutherford Appleton Lab

LSC, March 2004

LIGO-G040058-00-K

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Contents

• Report– Motivation– Background– Results– Next steps

• Discussion– Is this the right way to go?– Any caveats etc?

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Background

• Norna (ALUKGLA0010) showed that the isolation in the quads (and triples?) will be OK provided that the internal modes of the different blades are high enough and do not coincide.

• Ken went on to assert (ALUKGLA0007) that high enough meant about 40 Hz.

• Picture from Norna.• Will the blades give adequate isolation?• In particular, will the peaks in transmissibility caused

by the internal modes overlap?• And what is the effect of the mass of the wire clamps?

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From Norna’s paper:

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• So – find the actual transmissibility of the blades and multiply by the curves above (updated). (Even better, reproduce the curves above PLUS blade internal modes).

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Run through T040024

• Modal analysis of reference blade• Modal analysis of blade from Conceptual design• Harmonic

– No damping (cf Norna’s plot)– With damping, various damping ratios

• Test effect of changing alpha on internal modes• Prestress• Add wire• Effect of wire clamp mass

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T040024

• Pretty simple stuff over Christmas• Uses ANSYS macro language for ease of “what if”

scenarios• Simple to write macros so that a command of the

form – bf1,.48,.0045,.096,.01,20,1,1000,.050,11

• Will find the eigenvalues of a blade 0.48m long, 0.0045 thick, .096 root width, 0.01m tip width, find up to 20 eigenmodes in the range 1 to 1000 Hz, with .05kg wire clamp and 11kg mass.

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T040024

• ANSYS will find– Eigenvalues and normal mode shapes– Transmissibility in a given frequency range and

linear frequency step

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What equations is the FE solving?

• Modal analysis

• Harmonic analysis

• Damping

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FE equations

• So, use 1/(2Q) as the damping value in the ANSYS DMPRAT command.

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Modal analysis of reference blade

• Modal analysis of “reference” blade• Frequency has been measured at 55 Hz

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Modal analysis of blade from Conceptual design

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Effect of adding mass at blade tip

• 11 kg mass at blade tip

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Harmonic

• No damping• With damping, various damping ratios

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Harmonic – with damping

• “Zoom in” on peak by specifying restricted frequency range

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Extended frequency range

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Varying damping ratios

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Test effect of changing shape on internal modes

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Varying length and root width - 1

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Varying length and root width - 2

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Prestress

With Without

Little/no effect, as expected

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Add wire

Wire constrained laterally

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Mode shapes

Do any of these tie up with this peak?

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Effect of wire clamp mass

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Note T040025

• Revised dimensions• Easy changes allows look at a set of blades• NB resolution of peak• Results so far

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T040025 - Model

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Resolving the peaks…

• All three blades are analysed at a background range plus an “zoom” range for each one:

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T040025 – typical results

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Next

• So far – simply testing out the methods + tools• Next – get more detailed/serious

– Reference to this group – am I doing anything silly?– Check this method can reproduce Husman results– Get latest blade/wire dimensions– Check transmissibility vs measurements

• Calum’s thesis?• Elsewhere?

– Cross check with more detailed FE models (RAJ, MPL, others?)

– Explore effect of clamp mass again– Model sloping wires– What other effects to bear in mind?

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Discussion points

• Reference to this group – am I doing anything silly?• Check transmissibility vs measurements

– Calum’s thesis?– Elsewhere?

• Cross check with more detailed FE models (RAJ, MPL, others?)

• Explore effect of clamp mass again• Does this include “Norna’s curves” or do those need

to be added in to the results?• What other effects to bear in mind?