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Update on calculations
1. Vacuum barrier stability: CERN to comment on the shape/force calculations presented last week
2. Tube sizes: not constrained by pressure requirements (see Wendell’s email)
3. Global model with pressure scenarios and mechanical conditions: SOTON presentation shared earlier in the week and in the following. CERN to advice how to proceed: modelling and design
4. Other calculations: CERN to advise
DFX Helium Vessel Global Model: pressure scenarios
Required by BS EN 13445-3 for cat3 pressure vessel using DBA
Cold vessel at PHe <= 3.5bar
DFX vacuum at 0<= PvDFX <= 1.5bar
SC-Link vacuum at 0<= PvLink <= 1.5bar
Cases PHe (bara) PvDFX (bara) PvLink (bara)
A1 3.5 0 0
A2 3.5 1.5 0
A3 3.5 0 1.5
Relevant scenarios of pressure combinations (A4-A6 uncessary due to lower loads)
DFX Helium Vessel Global Model: whole length and mechanical constraints
The model shall include the whole length to account for the bending of the L-shapeby 3.5bar inside the vessel
The stress distribution determined by the mechanical supports/constraints:
Vertical supportby the vacuum break
Cases Vertical Support Longitudinal Support Centring
B1 Fixed Yes (No?) No
B2 Fixed Yes (No?) Yes
B3 Roller Yes (No?) Yes
B4 Roller Yes (No?) No
Longitudinalsupport
Centring support
Longitudinalsupport
DFX Helium Vessel Global Model: longitudinal is necessary
With out the longitudinal support:1. When the warm flange of the vacuum break is fixed, the stress on
the vacuum break braces is too high
2. The longitudinal support is a must if the warm flange is only fixed in the vertical direction (horizontal roller). Otherwise the bellows will extend too much under the 3.5bar insider the vessel
A1+B1(No Longitudinal)+Warm
Fixed
DFX Helium Vessel Global Model: Mechanical support options
B1 (CERN): Fixed vertical support on the warm flange of the vacuum break
Cases Vertical Support Longitudinal Support Centring
B1 Fixed Yes No
B2 Fixed Yes Yes
B3 Roller Yes Yes
B4 Roller Yes No
B3 (SOTON): Vertical support on the warm flange of the vacuum break can slide horizontally
FEM Modelling
Materials using linearized elastoplastic constitutive relations for direct DBA as specified by BS EN 13445-3.
Thermal deformation coupled for combined thermal stress
DFX Helium Vessel Global Model: A1+B1 Cold
DFX Helium Vessel Global Model: A1+B3 at 3.5bar
A1+B1 has more stress on the vacuum break braces than A1+B3, where the warm flange on the roller slides by 2mm to ease the tension
DFX Helium Vessel Global Model: A2+B1 Cold
DFX Helium Vessel Global Model: A2+B3 Cold
A2 has abnormal pressure of 1.5bara in the DFX vacuum, resulting in a upwards force on the DFX cold vessel. Stress is lower for both A2+B1 and A2+B3, although the latter is still better.
DFX Helium Vessel Global Model: A3+B1 Cold: not converged
Missing colours exceeds 150MPa
DFX Helium Vessel Global Model: A3+B3 Cold
A3 has abnormal pressure of 1.5bara in the SC-Link vacuum resulting in a downwards force on the DFX cold vessel. Stress is higher for both A3+B1 and A3+B3, the former does not converge in the solution and the latter is within stress and plastic deformation limits.
Conclusion:
Global model analysis shows mechanical support configuration B3 is necessary for the pressure vessel tests/operation requirements
Configuration B1 suffers more stress and potentially unstable under A3 condition
DFX Helium Vessel Global Model: A4(1.5bar)+B1 Cold
DFX Helium Vessel Global Model: A4(1.5bar)+B3 Cold
Smaller Horizontal Section
Orthotropic equivalent bellows so far
Smaller bellows need strengthening
Similar behaviour to large horizontal section
Cold at 3.5bar: Fixed (A1+B1)
Cold at 3.5bar: Roller (A1+B3)
Cold at 1.5bar: Fixed A4+B1 (not converged)
Cold at 1.5bar: Roller (A4+B3)