FEA History: Lower Structure

model no. Geometry Boundary condition in FE Model 1st 2nd 3rd 4th(Ansys)

3Assembly Rig only - no bracing or stiffeners added

All nodes on uppermost surface FULLY CONSTRAINED

35 - - -

Longitudinal (x) Transverse (y) 1st torsional

4Addition of 2 x sml cross braces, 1 x strap, 1 x large X-brace


93 100 150 185


5

Addition of members to approximate a similar geometry used by Tim Hayler (Nov04)


62 96 103 185


6Addition of the 2 x sml cross braces (as used in 4), to the geometry used in 5


92 100 140 185


7

Bracing added from implementation ring down to ~ penultimate mass in longitudinal direction


94 132 176 188

Transverse (y) Longitudinal (x) 1st torsional

MODE FREQUENCIES

FEA History: Lower Structure

Table 1: Early results (from ANSYS Worbench 8.0)

Model 4

1st mode= 93Hz

2nd mode= 100Hz

Model 5

2nd mode= 96Hz

Bracing added in locations that mimic approach the approach used by Tim in November

Model 6

1st mode= 92Hz

Addition of bracing as circled above (as was used in model 4)1st mode (longitudinal) increased by 30Hz2nd mode (transverse) of 100Hz

Model 7

1st mode= 94Hz

Quick addition of bracing as circled above 1st mode now in transverse direction

Graphical accompaniment to Table 1

8 as in model 7All nodes round the edge fully constrained

90 128 172 186


9

Moving the location of the bracing further down below the penultimate mass (lonitudinal only)


88 126 138.82 153

Transverse (y) Longitudinal (x) 1st torsionalcrossbraces

moving!

10

Bracing from implementation ring down to ~ penultimate mass in longitudinal and transverse directions


120 152 186 204


11 As above see pic 94 115 154 192


12 As above see pic 96 126 161 197


13 Shortened structure!All nodes on uppermost surface FULLY CONSTRAINED

140 152 187 222


FEA continued….

Table 2: further results from ANSYS

Model 8

1st mode= 90Hz

Change in BC’s in model – constraining all nodes round edge of top surface1st mode goes down

Model 9

2nd mode= 126Hz

Quick change - lengthening of braces to support further down the structure1st mode still in transverse (88Hz)2nd, 3rd, and 4th modes all in the lengthened braces as shown above

Model 10

Addition of bracing to increase the Transverse modeThe following two models involved using the same geometry, changing the combinations of displacement constraints used at the top of the lower structure

1st mode= 120Hz

Model 13

Shortening of overall length of lower structure used in model, following assessment of overall structural dimension in SoildWorks

(Reduced height in location shown above! Initial numbers had stemmed from limitations set by )

1st mode= 140Hz

Graphical accompaniment to Table 2

*Most recent Model of Lower Structure*

Boundary Conditions:

Uppermost surface of implementation ring fixed in all DOF

Mesh: (in Workbench 8.0)

Default setting: Global Control – basic, Relevance: -100

nodes:119 957, elements: 60 139

*Results: Most recent model of Lower Structure*

(nodes:119 957, elements: 60 139)

1st Mode: 128 Hz (transverse - see pic below)

2nd Mode: 140 Hz (longitudinal)

3rd Mode: 166 Hz (1st Torsional)

4th Mode: 214 Hz (2nd Transverse)

Model Geometry: Lower Structure….General comments/assumptions/

Limitation:

Model Geometry creates a ‘uniform transition’ between the basic structure and stiffening members at all joins (as highlighted opposite)

•consciously left in additional material in locations where further detailing is ongoing

•all bracing member as solid bars so far (for speed)

Planned change/improvements: Lower structure

•Widening of footprint to improve improve access (in progress)

•Fcomplete the detail at all connection locations (I.e. with clamps/stiffeners etc) to mass

FEA History: Lower Structure

Documents

uppermost surface

aluminiumall nodes

large xbraceall nodes

transverse directionsall

stiffeners addedall

tim hayler nov04all

sml cross braces

implementation ring