Probing of the Vertical Structure of the lower Atmosphere ...
FEA History: Lower Structure
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Transcript of 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
All nodes on uppermost surface FULLY CONSTRAINED
93 100 150 185
Longitudinal (x) Transverse (y) 1st torsional
5
Addition of members to approximate a similar geometry used by Tim Hayler (Nov04)
All nodes on uppermost surface FULLY CONSTRAINED
62 96 103 185
Longitudinal (x) Transverse (y) 1st torsional
6Addition of the 2 x sml cross braces (as used in 4), to the geometry used in 5
All nodes on uppermost surface FULLY CONSTRAINED
92 100 140 185
Longitudinal (x) Transverse (y) 1st torsional
7
Bracing added from implementation ring down to ~ penultimate mass in longitudinal direction
All nodes on uppermost surface FULLY CONSTRAINED
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
Transverse (y) Longitudinal (x) 1st torsional
9
Moving the location of the bracing further down below the penultimate mass (lonitudinal only)
All nodes on uppermost surface FULLY CONSTRAINED
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
All nodes on uppermost surface FULLY CONSTRAINED
120 152 186 204
Transverse (y) Longitudinal (x) 1st torsional
11 As above see pic 94 115 154 192
Transverse (y) Longitudinal (x) 1st torsional
12 As above see pic 96 126 161 197
Transverse (y) Longitudinal (x) 1st torsional
13 Shortened structure!All nodes on uppermost surface FULLY CONSTRAINED
140 152 187 222
Transverse (y) Longitudinal (x) 1st torsional
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