ITER Vacuum Vessel Supports - ENEA Vacuum Vessel... · ITER Vacuum Vessel Supports Intermediate report Contract EFDA – ENEA n° 07/1702 - 1541 Andrea Capriccioli . FPN FUSTEC doc

FPN FUSTEC doc. FUSTEC-TVV-CKSUP-001 Rev.0 page 1 of 49

FPN FUSTEC Frascati, 10 August 2007

ITER Vacuum Vessel Supports

Intermediate report

Contract EFDA – ENEA

n° 07/1702 - 1541

Andrea Capriccioli



Outline

Abstract pag.3 1. Forces evaluation pag.4

2. VV supports actual design pag.6

2.a) Forces evaluation;

2.b) Sizes and degrees of freedom;

2.c) Toroidal restraint system;

3. Vertical Supports alternative solutions pag.11

3.a) flexible plates;

3.b) “pendulum” W7-X style

3.c) “connection rods” Ignitor style

4. Toroidal Supports alternative solutions pag.25

4.a) “pendulum” W7-X style.;

4.b) central guide;

4.c) flexible plates.

5. Clamping sleeves Kostyrka pag.33

6. Conclusions pag.34

References pag.35

Appendix 1 (AGOM pot bearings) pag.36

Appendix 2 (Alternative solution: connection rods and flexible plates) pag.47



Abstract

In the ITER experimental Tokamak reactor, high currents flow in the Vacuum Vessel (VV)

during Plasma disruptions. The interaction between these currents and the toroidal-poloidal

magnetic field produces high local forces. The direction of the electromagnetic forces acting on

the VV can be upward or downward, while horizontal net force arises from the plasma tilting:

their combination with the VV dead weight gives resultants both in vertical (up or downward)

and horizontal directions.

The VV supports have to withstand all these forces, allowing only the slow radial displacements

due to the thermal expansion.

Other local forces appear around the ports (discontinuities in the VV shell) during the pulse:

these last forces have null resultant but produce local moments and ports distortions.

The present work includes the evaluation of the reference design (see also the presentation in the

VV DR meeting in Cadarache on the 28th June 2007).

As a consequence of the previous activity, alternative proposals will be evaluated: the main

differences consist in “bidirectional” vertical supports (working in up/down directions) and in

metallic components (avoiding elastomers or in general organic materials). In this case there are

no problems with radiations, temperature, vacuum conditions.

In the present work a first identification and a preliminary analysis of the proposed alternative

solutions have been performed.



20 MN13 m

12 mFz1

Fz2Fz3

Fz4

Fz5

40°

9.96 m

2.26 m6.50 m

Supp. n°1

n°5

n°4

n°3n°2

1. Forces evaluation

─ The total downward force on the VV supports, due to the weight, results equal to 90 MN;

─ The electromagnetic upward forces during VDE (III) result [1]:

● total VDE vertical force : 60 MN (by ampl. fact. 1.1; asymmetry peak = 2 MN)

● total VDE net horizontal force: 20 MN (by ampl. fact. 1.7; application point 11 m)

Fz5 = 6.5 MN Fz3 = 0.17*6.5 MN = 1.1 MN upward.

Finally, for the upward disruptions:

on each n°3 supports (3+symmetric) the total force results: 1.4 - 1.1 = 0.3 MN downward

and on the n°5 support the total force results : |10 - 6.6 - 1 - 6.5| = 4.1 MN upward

The force on the VV vertical support n°3

closest to the peak of the vertical force

results ≥ 10 - 6.6 - 2 ≥ 1.4 MN downward

due to the vertical forces only.

The total net horizontal force results 20 MN,

90° rotated with respect to the max vertical

peak (see the figure on the right side).

In this case the max vertical (z) upward

contribution, due to the net horizontal force,

results:

2 *F z1 *1 2 + 2 *F z2 *6 .5 0 + 2 *F z3 *2 .2 6 + 2 *F z4 *9 .9 6 + F z5 *1 3 = 2 0 *1 1 *1 .7F z1 = 0 .9 2 * F z5F z2 = 0 .5 0 * F z5F z3 = 0 .1 7 * F z5F z4 = 0 .7 7 * F z5

2 *F z1 + 2 *F z2 = 2 *F z3 + 2 *F z4 + F z5



For the downward disruptions we have to add the dead weight and the total vertical force of 72 MN

downward [1]. If the same vertical amplification and the peak factors are applied, we obtain a vertical

force equal to 10 + 72/9 *1.1 + 2 = 20.8 MN downward.

In this case the application point of the net horizontal force (25 MN) is not clear and it isn’t possible to

calculate its contribution to the vertical compression.

A reference value of 22 MN can be assumed as first approximation.

Summarizing, the VV supports must bear vertical forces from 4.1 MN upward to ≈22 MN downward.



2. VV supports actual design

2.a) Materials

• TEFLON

Teflon is the DuPont trade name (PTFE: Poli Tetra Fluorine

Ethylene ) and/or Fiberslip: are material typically used

when the radiation dose results lower then 106÷107 rad

(DOE Handbook – Design Considerations - 1132-99 –April

1999).

In ITER a peak dose to the pad of 0.22 106 rad is estimated

(to be carefully checked). If higher doses would occur

additional shields could be necessary (Teflon/Fiberslip

contains Fluorine and under radiation could produce

sulphuric acid if Oxygen or Hydrogen are present).

• NEOPRENE

Neoprene is the DuPont Performance Elastomers trade name for a family of synthetic rubbers

based on polychloroprene. On the market several types of rubber insulators/ supports are

available (see figures next page – AGOM company only for example).

These kind of bearings can carry very high loads (>50 MN) and are designed for combined

vertical plus horizontal loads (≤15% of the max vertical load). Rotations ≤ ±0.01 radiant are

also allowed.

The average contact pressure should be less than 20 N/mm2 with max value ≤ 40 MPa . The

ITER VV dead weight results about 10 MN per support and a diameter of 800 mm is enough to

take only this load. If the VDE downward vertical forces are considered (VDE III Slow) the

compression can reaches 22 MN (see Chapter 2. Forces evaluation). In this case the diameter

should be ≈ 1.5 m.

In Appendix 1 the AGOM pot bearing catalog and technical data sheet are reported.

Both Teflon and Neoprene could need of an active temperature control.



[1] Design Description Document -DDD15- Vacuum Vessel - September 2004. Pag.107



2.b) Sizes and degrees of freedom

The limit seems to be the maximum pressure (≤40 MPa) on the Neoprene: this involves large

dimensions of the pot bearings. The first solution could be to double the number of supports.

In this last hypothesis, the diameter of each support results close to 1 m (1.5/√2).

About the degrees of freedom, in a cylindrical reference system, the slow radial VV thermal

expansion must be guaranteed; all the other displacements (toroidal, axial and fast radial too) should

be restrained.

The elements in order to assure this task are the VV supports: they should have a “bilateral

behavior” (up/down effect in vertical direction).

To obtain a “bilateral behavior” of the actual vertical supports, groups of “ropes” without preload

were used. But the preload is necessary because, when an upward disruption occurs (4.1 MN

upward), a detachment with the consequent impact between VV feet and bearing pads will increase

the local pressure on the Teflon and Neoprene pads. This behavior is generally avoided using

preloaded systems.

In this case it’s possible to preload the ropes without influence on the bearing pads; the rough sketch

shows an example of possible solutions [3]:

INCONEL SA-637 Gr

ASTM A453 Gr

Preloading system: some examples (wedges; thread link)

The point is that the ropes preloading is

practically equivalent to rigid rods (easier

and chipper).

A more efficient system could be the use of

“dumpers”, instead of ropes or rods.

The only note regards the absence of a

vertical displacement amplification.

It should be necessary to verify the

pressure transient on the bearing pads

during the VDEs and increase the dampers

efficiency, with the same system used for

the radial restraints (vert.+hor.levers – see

the figure below).



The first intermediate conclusion of the previous evaluation is the adequacy of the sliding bearing pads

and the neoprene use to the ITER compression loads.

The limit seems to be the size necessary to place the bearing pads themselves and the systems to avoid

VV vertical displacements during upward VDE.

A minor change regards the introduction of two spherical joints in the radial arm connection between

VV and horizontal lever.

Vertical lever

Horizontal lever Radial arm

Vertical link

Dampers

Bearing

Vertical ropes

Other point is the radial arm configuration:

- the radial arm is subjected to bending (at

least a “spherical joint” is necessary);

- the radial arm cooperates with the toroidal

restraints against rotations around a local

vertical axis. To make free the radial arm

from the vertical rotations also, it’s

necessary a design review linking the

support with the horizontal lever through

two spherical joints.



2.c) Toroidal restraint system

In the actual design a couple of toroidal restraints

are added under each lower port.

This configuration, where the port is placed

between two elements, seems to be particularly

critical.

The main reason is the possibility to reach the

seizing in some conditions (port thermal

expansion, vertical displacements, influence on

the vertical reaction forces, port rotations, etc.). The seizing of only one port can lead the whole VV

to lose its central position and to increase the bending stress on the perpendicular ports.

Only large tolerances could avoid the seizing probability, leaving the VV free to move radially yet.

The possibility to change with continuity the toroidal stiffness of the restraint system (in this case

through the vertical displacement of the VV) is an element that can be preserved with other systems,

without the disadvantages shown in actual solution.

The toroidal restraint systems that seem to fit well with actual geometry are both the “central rail”

and the “pendulum” solutions.

With both the previous systems it’s possible to change the stiffness with continuity and a brief

explanation will be presented in the second part of the present document (see Chapter 4).



3. Vertical Supports alternative solutions

Three alternative solutions were analyzed, as first

approximation (the radial restraint against fast horizontal

forces remains necessary for all; only the introduction of two

spherical joints between the radial arm and the horizontal

lever is required).

The first alternative solution is the use of flexible plates both

as vertical and toroidal restraint. A brief parametric analysis is

shown in Tab.1 next page. The first results seem not to

exclude the possibility of vertical plates with a total height

lower than 1000 mm. Other structural analyses are necessary

to take into account all the loads and/or displacements.

The second alternative solution is the use of spherical joints

both for vertical and toroidal restraint (type W7-X).

Some analyses were performed, but other analyses are

necessary to verify if 9 vertical supports are enough to support

the vertical reference max load (22 MN downward).

For the toroidal restraint with spherical joints no analyses

were performed (no problems seem to be).

The third alternative is the use of Connection roads (type

Ignitor) for the vertical supports and flexible plates (or central

guide) for the toroidal restraint.

Some analyses were performed and the results are shown in

the following pages.

Flexible plates for vertical and toroidal

supports

Spherical joints forvertical and toroidal

supports

Connection rods andflexible plates or central guides


FPN FUSTEC Frascati, 10 August 2007 Tab.1

3.a) flexible plates

Plates thicknesses [mm]

Net height (Total=Net+300 mm)

N° of plates / total width

Max SEQV [MPa] * F=22 MN; rad displ=40 mm

Radial Reaction Force [MN] full support (40 mm)

24/32 1650 8 / 336 147 / 220 (tot: 345) 0.212

20/26 1350 8 / 288 179 / 269 (tot: 422) 0.221

13/18 1050 12 / 336 186 / 295 (tot: 454) 0.200

7/15 750 22 / 484 183 / 304 (tot: 461) 0.149

Common tangential length = 950 mm

Gap between plates =10 mm

NO VDE TANGENTIAL FORCES – NO MOMENTS (around Vertical and Toroidal axes) – NO Buckilng

*UX >< 0 (if UX=0 stress picks are present at the 4 corners: for example 147 ⇒ 241)

Tick.1

Tick.2

Grounded or fixed elements

Loaded elements

X



3.b) “pendulum” W7-X style

The pendulum system in the W7-X reactor was possible because the vertical supports constrain only

vertical displacements (downward).

The W7-X Plasma Vessel is free to move on the horizontal plane, both with the previous plane

sliding design and the actual spherical “pendulum” system. As result of this, an auto centering

system (ACS) was possible as the easiest way to leave the PV free to expand, keeping its centre.

It’s to note that, with the selected vertical supports, a rotation of all the PV around the vertical axis,

can be allowed.

Another important point is the absence of electromagnetic forces on the PV: the dimensioning of the

ACS was performed to balance the forces from the vertical supports friction coeff. and the elastic

reaction of the connections (bellows) between PV and Cryostat.

In case of not “sliding” vertical supports, the only free degree of freedom is the radial one (in a

cylindrical ref. sys.). This means that a toroidal “pendulum” system (with the stiffness necessary to

withstand the VDE forces) goes in contrast with the vertical ones.

For this reason the toroidal ”pendulum” system is compatible only with the spherical vertical

supports (or, in general, with “sliding” supports). The analysis of this last type of supports is not part

of the present document but a first dimensioning step is reported in the next pages.

Only for example purpose, the figures below

show the “pendulum system (only for

compression forces):

Spherical joint: inner pendulum plus external

shells (total height remains 780 mm)



Inner pendulum: the diameter of the two

spherical joints is 400 mm and the height of the

cylinder connecting the two half spheres, is

210mm.

View of the inner spherical side of the lower

pendulum support:

In the following pages preliminary stress analysis results are reported.

The aim of the analysis is only a first evaluation of the stresses level and the reaction friction forces.

A further detailed analysis with the real maximum acceptable dimensions should be necessary.

Basic point is the right definition of the friction coefficient between the two half parts of each spherical

joint, to minimize the reaction friction forces: in this case the conservative value of 0.2 was set.

As preliminary result, a double number of supports could be the first feasible solution.



The following figures show the system sliding (with a friction factor = 0.2) under the VV dead weight,

as vertical load, and a radial displacements of 1 mm. The reaction force due to the friction between

inner spheres and outer spherical housings results now about 3 MN (per each vertical support).

In this case, the max SEQV results about 370 MPa in the cylindrical connection (see the two figures

below).

The max SEQV stress results of 738 MPa, with this dimensions: to decrease the maximum value it

should be necessary to increase the diameter of the cylindrical connection and the total height of the

joint. This last point it’s also necessary to insert the other halves of spheres to give a “bilateral”

behavior to the joint itself.





3.c) “connection rods” Ignitor style

A general support scheme, designed for

Ignitor reactor, is shown in fig 1 and the cross

(a) and longitudinal (b) sections are shown in

fig.2: only one sector 174 mm width is visible

in the section (b). The total number of sectors

will be defined on the basis of the maximum

vertical load and materials properties. The

distance between the two rotation centres (400

mm) has been defined to have a maximum

vertical displacement < 2mm during baking

(40 mm max radial displacement [2]).

fig. 1

380+

10 m

m

40

5020

0 m

m

220 mm

60

20

780

mm

140

50

380 mm

(a) (b)

84 4242

60

φ140

mm

50

3 3

174 mm

10

fig.2



The maximum height results of 780 mm that should be available between the pedestrian ring and the

green zone of the lower port (see fig. below and the yellow rectangle that schematizes the connection

rods vertical supports area).

An ANSYS model of half sector was performed to evaluate the stresses in the components (forged

external shell, connection rod, cylindrical insert).

Fig. 3 next page, shows the model with the components and the main geometrical dimensions.

Vertical lever

Horizontal lever Radial arm

Vertical link

Dampers

Bearing

Vertical ropes



42

45

400

87

780

6060

640

220140

20

380

fig. 3

Nodes with applied Vertical Force

Grounded nodes

Symmetry plane

Symmetry plane

ANSYS FEM model:

The external forged shell is ASTM-A 453 Gr 660 while the connection rod and cylindrical inserts are in

INCONEL 718.

A total vertical force

downward of 22 MN [2]

was applied to the vertical

support: this load requires 8

modules (fig.2 shows only

half module).

A preliminary structural

analysis is shown in the

following pages.



Vertical displacements UY (mm) in CSYS 0

Material Prop.:

ASTM-A 453 Sy0.2=589 MPa (RT)

Su=893 MPa (RT)

Sm = 295 MPa (RT)

Sm = 451 MPa (77 K)

INCONEL 718 Sy0.2=1010 MPa (RT)

Su=1246 MPa (RT)

Sm = 667 MPA (RT)

Sm = 863 MPA (77 K)

Inserts displacements (x200) [mm]



von Mises stress (MPa)




The zone of max stress (377 MPa) is in the forged shell and (512 MPa) in the connection rod: the results

seem to be acceptable compared with only (Pm+Pb) at RT <1.5 Sm = 442 MPa (ASTM-A) and 677

MPa (Inconel).

The following figures show the system sliding (with a friction factor=0.2) under the VV dead weight, as

vertical load, and a radial displacements of 1 mm. The reaction force due to the friction between

connection rod and cylindrical inserts results about 0.84 MN (per each whole vertical support formed by

8 modules).

In this case the max SEQV results of 287 MPa in the connection rod (see the two figures below).




Displacements USUM [mm]

von Mises stress [MPa]



87

87

In the real manufacturing the

forged shell (part A in fig.1) will

be a single forging piece and all

the parts (connection rods

included) will be drilled together

and at the same time.

The figure on the right side

shows two halves (87 mm

width) and the next figure

shows the single module 174

mm width. Clearly the division

in “modules” is for calculation

purpose only.

174

780

20

380

n° 8 units

(1400 mm)



M

4. Toroidal Supports alternative solutions

4.a) “pendulum” W7-X style

When the vertical supports allow toroidal displacements, as in actual bearing pads solution, the

“pendulum” restraint system seems to be a really good choice.

The figures below show the W7-X Auto Centering System [2].

In the W7-X reactor no electromagnetic forces act on the Vacuum

Vessel and the “pendulums” stiffness is not a critical point.

In the figure below it is possible to note the relative high L/D ratio

The system allows Vacuum Vessel vertical displacements and

radial thermal expansion with small toroidal rotations of the whole

VV itself.

The “pendulum” solution for ITER reactor has to take into account several basic points:

- the presence and the entity of the net horizontal force;

- the presence of the radial restraint system;

- during the disruption event, the opportunity to spread the reaction forces with different weights

between radial and tangential ports (to minimize the stress level in the Ports-VV connection).



VV

Pedestal ring

At the moment no possibilities there are to perform a detailed design and analysis of a proper toroidal

restraint style W7-X.

Only a scheme of “pendulum” with variable axial stiffness is shown in fig 4:

Fig.4

It will be possible to change with continuity the axial stiffness at constant pendulum length, if the

screws pitches are identical.

This could be fixed on one end to the lower port and on the other end to the pedestal ring.

4.b) Central guide

A sketch of toroidal restraint with only one

central guide (or rail) is shown in the figures:

In this case the possibility to reach the seizing is lower than the actual design, and the same toroidal

stiffness variability (with VV vertical displacement) is maintained.



4.c) Flexible plates

The flexible plates could be used for toroidal restraint

only; the scheme of the cross section is shown in fig.5: the

total number of plates will be defined on the basis of the

maximum toroidal load and materials properties.

If we consider a net horizontal force of 20 MN (VDE III

slow) [1] and the fault of all the radial restraints (worst

fault condition), the max tangential force occurs in the two

toroidal supports closest to the plane perpendicular to the

axis of the horiz. force.

100

mm

780

mm

100

mm

300 mm

300 mm

10 mm

8 mm

272 mm

60 mm

fig. 5

Ft1

Ft2

Ft3

Ft4

Ft5

40°

x

f

f

f

f

f

20 MN

Toroidal restraint

Vacuum Vessel and Ports

In the scheme left side, the max

force occurs in the toroidal support

n° 3 (and symmetric).

In this hypothetical worst condition

the max force results of 7.6 MN

and 10 is the total number of plates

per each toroidal support.



The figure below show the group of 10 plates 10 mm thick (without the “heads” in the yellow zones:

grounded and loaded parts). The gap between each plate is 8 mm and the total radial width will be about

270 mm (if other 50mm as initial and final “heads” radial thickness can be assigned).

The figure on the right shows

the ANSYS FEM model of

the single plate in INCONEL:

In the figure next page the

single plate and its global

dimensions are reported.

Grounded region 10 mm thick

Loaded region 10 mm thick (tangential forces)

Central flexible region 8 mm thick

Lateral flexible regions 10 mm thick



Displacements (x10) [mm]

All the degree of freedom are

blocked in the lower part of the

plate while the upper part can

slides only along the tangential

(Z) axis only. No moments

around vertical axis have

been applied.

A preliminary structural

analysis of the single plate is

shown below:

1400 mm

60 mm grounded

60 mm loaded



SEQV stress middle section [MPa]

SEQV stress top position [MPa]



The stress in the middle of the shell thickness results very low = 201 MPa with a Sm = 451 MPa, while

in the shell top position (membrane+bending) there are local values of 852 MPa. In these 4 nodes the

high level of stress is due to a stress concentration and a factor 3 can be applied in these points for peak

values (moreover the previous results have been obtained for the worst fault conditions, at RT and

without proper design rules).

During baking, displacements of 40 mm radially and max 2 mm vertically are expected. In this situation

each toroidal support (10 plates) reacts with a vertical force of 0.62 MN and a radial one of 0.34 MN.

SEQV top [MPa]

40 mm

2 mm



SEQV mid [MPa]

The stress of the plates results mainly from bending: 580 MPa (against 60 MPa in mid sec). This value

results less than 1.5 Sm = 677 MPa (at RT).

Clearly the initial position of the vertical supports can be set to obtain the connection rods in vertical

position during operation (VV temperature =100°C): in this case both at RT and baking temperature

(200 °C) the max vertical displacement results of 1mm instead of 2. In this last configuration the

vertical force decreases to one half and the max stress to 530 MPa.

In this first solution the global restraint system consists of vertical supports (connection rods) and

toroidal supports (flexible plates): both the systems cooperate to take the vertical force (up or

downward) during VDE event.



5. Clamping sleeves Kostyrka

A possible alternative to the dumpers (hydraulic or mechanical) are the “clamping sleeves”. The figure

below shows the very simple item with the central axis and the external sleeve.

When the hydraulic chamber inside the sleeve is under pressure, the elastic membrane presses on the

cylinder, blocking it.

During the pulse the VV remains blocked and it can expand after, completely free.

For a reference diameter of 100 mm per 200 mm length, each sleeve is able to support 0.3 MN.



6. Conclusions

1. The bearing pad solution, as Vertical support system, results acceptable for

the maximum load. The limit is the large size and to double the number of

supports seems to be a feasible solution (see Appendix 1).

2. The replacement of the ropes with other system (rods or dampers) doesn’t

involve complex design review (nevertheless further analyses are necessary) .

3. The actual Toroidal restraint system shows potential risks. The proposal of

the “pendulum” system seems to be the right choice: a further detailed

analysis is recommended. The other typology (central rail and flexible

plates) are feasible if in accordance with the selected vertical support system.

4. The alternative solution for the Vertical supports with “connection rods”

seems to be achievable but the space allocation in the toroidal direction has

be verified (see Appendix 2 also).

5. The solution with spherical joints (W7-X type), as Vertical supports, could

be analyzed too (high reaction forces by friction) but higher vertical space

seems to be necessary. To double the number of vertical supports can be

another possibility.

6. The Radial restraint system (with secondary implementations) remains

basically unchangeable and common to all the actual and proposed systems.



References

[1] Design Description Document - DDD15 - Vacuum Vessel - September 2004

[2] A. Cardella “ITER Vacuum Vessel Support System”, ITER Vacuum Vessel Design Review

Working Group Meeting, Cadarache 28 June 2007

[3] A. Capriccioli “ITER VV Vertical Supports”, presentation at the Working Group Meeting -

Cadarache 28 June 2007



APPENDIX 1























APPENDIX 2

Alternative solution with connection rods as vertical supports

and flexible plates as toroidal restraint

In this solution the global restraint system consists of vertical supports (connection rods) and toroidal

supports (flexible plates): both the systems cooperate to take the vertical force (up or downward) during

the vertical plasma disruption event.

The radial support system (radial arm, horizontal and vertical levers, dumpers etc.) has to be translated

upward (through the part ocgs) to intercept the radial forces coming from the ports.

In the figure below, a rough scheme shows the global system:

To explain the meaning of the central rail, it’s necessary to note that, when a net horizontal force pushes

the VV in its same direction, the ports bend and rotations around local vertical axes occur. As a result of

that, high stress will appear in the VV-Ports connection zone (see the reinforcement proposal;

Cadarache 28/06/2007).

Pedestal ring level

VV lower ports level

Radial arm with spherical connection

Horizontal lever

Central rail

ocgs



The following figure shows a rough scheme of the ports distortion:

Both the proposed supports show lability against these rotations (in the actual reference design the

moment should be partially balanced by only one -of the two per ports- toroidal supports and by the

connection radial arm / horizontal lever).

In the present alternative design, the radial arm

itself and the vertical translation support have been

used to insert a central guide. This guide and the

toroidal support help the Ports to take the VV,

decreasing both the maximum stress level of the

VV-Ports connection and the VV horizontal

displacement (see the fig. on the right) and avoiding

the connection rods to support dangerous rotations

around a vertical axis.

In this case the stiffness ratio (~20% between the

toroidal and radial supports stiffness) changes,

because the stress passes from the VV-Ports

connection to Ports-Supports system .

F

F



icgs

a

b

Easier than the previous scheme and with similar characteristics is the following:

the only difference consists

in replacing the group of

flexible plates with another

central guide system (icgs–

inner central guide system).

Clearly, as in the outer

central guide system,

proper vertical gap will be

foreseen between the parts

(a) and (b).

If the guides show evidence

of problems with reference to

the sliding assurance, two

half groups of flexible plates

can be used.

In this case also, other

analyses are necessary to

evaluate the effects of

horizontal displacements

induced by the ports bending,

during the VDE.

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