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FEA History: Lower Structure

FEA History: Lower Structure. Table 1: Early results (from ANSYS Worbench 8.0). Model 5. Model 6. Model 7. Model 4. 1 st mode = 93Hz. 1 st mode = 92Hz. 2 nd mode = 96Hz. 1 st mode = 94Hz. Bracing added in locations that mimic approach the approach used by Tim in November.

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FEA History: Lower Structure

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  1. FEA History: Lower Structure Table 1: Early results (from ANSYS Worbench 8.0)

  2. Model 5 Model 6 Model 7 Model 4 1st mode = 93Hz 1st mode = 92Hz 2nd mode = 96Hz 1st mode = 94Hz • Bracing added in locations that mimic approach the approach used by Tim in November • Addition of bracing as circled above (as was used in model 4) • 1st mode (longitudinal) increased by 30Hz • 2nd mode (transverse) of 100Hz • Quick addition of bracing as circled above • 1st mode now in transverse direction 2nd mode = 100Hz Graphical accompaniment to Table 1

  3. FEA continued…. Table 2: further results from ANSYS

  4. Model 9 Model 10 Model 13 Model 8 2nd mode = 126Hz 1st mode = 140Hz 1st mode = 120Hz 1st mode = 90Hz • Quick change - lengthening of braces to support further down the structure • 1st mode still in transverse (88Hz) • 2nd, 3rd, and 4th modes all in the lengthened braces as shown above • Addition of bracing to increase the Transverse mode • The following two models involved using the same geometry, changing the combinations of displacement constraints used at the top of the lower structure • 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 ) • Change in BC’s in model – constraining all nodes round edge of top surface • 1st mode goes down Graphical accompaniment to Table 2

  5. *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

  6. *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)

  7. 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)

  8. Planned change/improvements: Lower structure • Fcomplete the detail at all connection locations (I.e. with clamps/stiffeners etc) to mass • Widening of footprint to improve improve access (in progress)

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