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Structural analysis and verification of the ITER TF model coil test conditions
Fusion Engineering and Design 58 – 59 (2001) 247– 251 www.elsevier.com/locate/fusengdes
Structural analysis and verification of the ITER TF model coil test conditions S. Raff a,*, P. Schanz a, H. Fillunger b, B. Glaßl c a
Forschungszentrum Karlsruhe, Postfach 3640, D-76021 Karlsruhe, Germany b EFDA Close Support Unit, D-85748 Garching, Germany c Noell KRC, D-97076 Wu¨rzburg, Germany
Abstract An FE-model already used during the design of the test assembly consisting of the International Thermonuclear Experimental Reactor (ITER) Toroidal Field Model Coil (TFMC), the EURATOM LCT-coil and the Inter Coil Structure (ICS) was extended to allow for predictions of tests, which will be performed in the TOSKA facility. For the first test step, with the TFMC current loaded alone (single coil test), predictions are given for 80 kA, the design current. Because of some uncertainty in the friction behaviour between winding pack (WP) and coil case, a parameter study was performed describing the limiting cases of the coil behaviour. Since the mechanical sensors could be installed only on the outer coil case surface, the possibility of deriving from this information details of the internal coil behaviour also is discussed. © 2001 Elsevier Science B.V. All rights reserved. Keywords: FE-model; Inter Coil structure (ICS); Toroidal Field Model Coil (TFMC)
1. Introduction The TFMC which is under construction under the responsibility of the European Home Team will be tested in TOSKA, a facility for testing large superconducting magnets at Forschungszentrum Karlsruhe. Two steps are planned. First, the TFMC will be tested in its self field (single coil test) and afterwards in the background field of the European LCT-coil. In the past, the mechanical analysis concentrated on the design [1] and on the
* Corresponding author. Tel.: + 49-7247-82-3768; fax: + 49-7247-82-3718. E-mail address: [email protected] (S. Raff).
mechanical instrumentation [2,3]. Now, it is focussed on analysis for test preparation [4] and test predictions. For the test evaluation, the relatively simple single coil test is a favourite starting point since nearly no interferences with the other test rig components have to be expected, and the stress and deformations of the TFMC have some symmetries allowing certain sensor checks.
2. The finite element model To perform test predictions for the mechanical behaviour of the test assembly consisting of the two coils (TFMC and LCT-coil) and the ICS in between, a previous mechanical model developed
0920-3796/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 0 - 3 7 9 6 ( 0 1 ) 0 0 4 5 2 - 5
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S. Raff et al. / Fusion Engineering and Design 58–59 (2001) 247–251
by industry [5] was extended to describe the electromagnetic as well as the mechanical behaviour. Using the ‘multi physics’ FE-code ANSYS [6], the same nodalization could be used for both subjects, reducing the computational effort for the investigation of different loading cases. The newly added electromagnetic model consists of the two winding packs (WP) of the TFMC and the LCT-coil, using geometry and grids from the mechanical model. The resulting Lorentz forces at the grid nodes are the load input for the mechanical model. To obtain a suitable mechanical model (Fig. 1), some modifications were done concerning the LCT-coil WP, the TFMC supporting in the ICS, the contact elements allowing for friction at all interfaces, introduction of final design modifications, the real supporting structure and additional connections between the coils.
Fig. 2. The electromagnetic model and resulting magnetic field for the single coil test (iTFMC =80 kA, iLCT =0 kA).
3. Results for the single coil test
Fig. 1. The mechanical model with the model coil (TFMC) fixed in the inter coil structure (ICS) and the LCT-coil behind.
To perform the single coil test, an analysis was performed for the maximum design current of 80 kA. The maximum magnetic field of 7.0 T occurring locally in the curved parts of the racetrack form (Fig. 2) differs slightly from the results of more sophisticated models [4]. However, the resulting Lorentz forces depend only weakly on such local peak values. The calculated force distribution, which is symmetric in out-of-plane direction for this load case, produces maximum stresses of 170 MPa (Tresca stress intensity) in the casing and about 100 MPa (tangential) in the WP, both in the curvature near the surface of the inner bore due to bending effects caused by the coil expansion. The maximum value of the interpancake shear stress of the WP is about 17 MPa. These values are about 40% of the values calculated for the double coil loading case calculated for the design [1]. For all former analyses [5], zero friction between WP and coil case was assumed. Now fric-
S. Raff et al. / Fusion Engineering and Design 58–59 (2001) 247–251
249
Table 1 Influence of friction between winding pack and casing on coil deformation; single coil test of TFMC, i= 80 kA Friction coefficient
Maximum coil expansion (mm)
Outer joint region elongation a (mm)
Winding pack m max tan (%)
Winding pack | max tan (MPa)
Casing | max Tresca (MPa)
Casing | max tan (MPa)
0.0 0.3 10.0
2.38 2.15 1.99
1.04 0.80 0.70
0.095 0.092 0.085
104 100 91
173 161 169
167 160 172
a
Measured length 1.50 m (part of straight back leg).
tion has been considered. But since the friction behaviour is not known very well so far, a parameter study was performed with the limiting cases of zero friction and bonding. In the analysis, the latter was approximated using a high friction coefficient of 10 (Coulomb friction approach). In addition, a somewhat realistic coefficient of 0.3 was used. Table 1 shows the influence of friction on the horizontal coil expansion, the maximum values of stress in the coil case, the tensile stress and strain in the WP and the outer joint region elongation of the WP. It should be mentioned that friction might reduce the joint region elongation, which is a critical quantity of the coil [1], by about 35% at maximum. With the exception of the casing stresses, all given quantities show a systematic correlation to friction.
back leg-part housing the joints; (b) Strain gauges (rosettes) to determine the coil stressing; (c) Strain gauges (uniaxial) to determine the deformation of the coil case walls at a horizontal and vertical cut. A few selected predictions for the sensor values are shown in Table 2 depending on the abovementioned friction coefficients. For some quantities in the table, a rather clear dependence on
4. Sensor predictions and derivable information Since it was not possible, due to safety reasons, to install mechanical instrumentation inside the coil, the coil behaviour can only be observed by displacement sensors and strain gauges mounted on the outer coil case surface. Therefore, one important question is whether the measured values on the coil case allow for a reliable determination of the internal coil behaviour, e.g. the internal WP behaviour and the above-mentioned friction effects. Fig. 3 shows the sensor types and locations on the TFMC case. There are three groups of measurements: (a) Displacement sensors to observe the global coil expansion under load (horizontal and vertical) and the elongation of the straight
Fig. 3. Mechanical sensors on the coil case: strain gauge rosettes (GRI), strain gauges uniaxial (GEI) and displacement devices (GDI).
S. Raff et al. / Fusion Engineering and Design 58–59 (2001) 247–251
250
Table 2 Predictions for some selected sensors; single coil test, i =80 kA Friction coefficient
0 0.3 10.0 a b
Dl
a
Dl
b
|Tresca
|y
GDI773 (mm)
GDI771 (mm)
GRI820 (MPa)
GRI826 (MPa)
GEI839 (MPa)
GEI838 (MPa)
0.45 0.50 0.60
−0.33 −0.31 −0.29
145 142 148
77 84 100
67 60 21
−20 −18 −14
Measured length 1.50 m (part of straight back leg outside). Measured length 1.24 m (part of straight back leg inside).
friction can be seen, for others not. The clue for that lies in the contact behaviour between WP and the casing. Fig. 4 shows a cross-section through the coil (top: undeformed; bottom: deformed). Under current load, the WP is pressed on the outer case wall (outer ring) along the whole circumference, but between WP and the inner case wall (inner ring), a gap opens decoupling the WP from the casing to some extent. The coupling on the outer ring depends on friction. Thus, the sensor values measured near or on the outer ring will depend more strongly on friction than the quantities on or near the inner ring of the coil case. Comparing, e.g. the predicted elongations of the case along the outer joint region given by sensor GDI773 (Table 2, column 2), the value clearly increases with increasing friction. This has to be compared with the values from Table 1 for the WP elongation (column 3). In the case of high friction, the values of both tables should approach each other. The highest WP elongation occurs without friction, whereas the coil case elongation shows a reciprocal behaviour. Due to the gap, this cannot be observed at the inner joint region. Nearly no-friction dependence shows the maximum case stresses (Table 1). The predicted values for the stress sensor GRI820 lie near the same location (inner edge of vertical coil cross-section) and show no dependence, too. But the values of sensor GRI826 (Table 2, column 5) lying near the outside edge in the horizontal cross-section again clearly depend on friction. The uniaxial stress values (sensors GEI838 and 839), observing the deformation behaviour of the inner and outer ring
wall behaviour, can also be explained by the gap formation combined with wall bending effects due to the WP pressed on the outer coil casing part. In principle, for the interpretation of the measurements, this local dependent behaviour may help to estimate the influence of friction. E.g., the quantities with weak dependence on friction will
Fig. 4. Cross-section of undeformed (top) and deformed (bottom) TFMC (deformation scaling factor =70).
S. Raff et al. / Fusion Engineering and Design 58–59 (2001) 247–251
allow to determine the stress level of the coil whereas the relation of ‘friction-dependent’ values to ‘friction-independent’ values may allow to draw some conclusions concerning the actual friction effects.
5. Conclusions Predictions for the single coil test of the TFMC have been gained performing electromagnetic and mechanical analysis with an improved and modified FE-model. A special item of the analysis was to estimate the influence of friction between WP and coil case in order to assess the stresses in the WP. A parameter study showed the influence on some quantities that characterize the coil behaviour. The task of the test evaluation concerning the mechanical sensors will be to determine, e.g. the influence of friction on the coil behaviour by sensor values gained solely on the outer coil surface. The evaluation of the predictions at the sensor positions showed that this may be possible to some extent. Thus, the single coil test results will help to analyze the more complex coil behaviour in the following TFMC test in the LCTcoil field.
251
References [1] P. Libeyre, B. Crepel, P. Decool, H. Fillunger, B. Glaßl, U. Hoeck, R. Kreutz, R. Maix, R. Meyer, R. Penco, S. Raff, E. Theisen, N. Valle, From conceptual to engineering design of the ITER TFMC, Proceedings of the 20th SOFT, Marseille, France, 7 – 11 September, 1998, pp. 767 – 770. [2] A. Ulbricht, M.S. Darweschsad, J.L. Duchateau, H. Fillunger, S. Fink, G. Friesinger, R. Heller, P. Hertout, P. Libeyre, G. No¨ ther, S. Raff, F. Wu¨ chner, G. Zahn, The preparations for testing the ITER Toroidal Field Model Coil (TFMC), Proceedings of the 20th SOFT, Marseille, France, 7 – 11 September, 1998, pp. 739 – 742. [3] H. Fillunger, F.H. Hurd, G. Zahn, A. Ulbricht, P. Libeyre, E. Theisen, F. Beaudet, ITER TF Coil assembly, commissioning and instrumentation, Proceedings of the 21st SOFT, Madrid, Spain, 11 – 15 September, 2000. [4] J.L. Duchateau, H. Fillunger, S. Fink, R. Heller, P. Hertout, P. Libeyre, R. Maix, C. Marinucci, A. Martinez, R. Meyder, S. Nicollet, S. Raff, M. Ricci, L. Savoldi, A. Ulbricht, F. Wuechner, G. Zahn, R. Zanino, Test program preparations of the ITER toroidal field model coil (TFMC), Proceedings of the 21st SOFT, Madrid, Spain, 11 – 15 September, 2000. [5] B. Glaßl, Stress analysis of the inter coil structure ICS by a 3D FE programme, AGAN technical report TR-NO-004, Consortium AGAN (ACCEL, Bensberg, Germany; ALSTOM, Belfort, France; ANSALDO, Genova, Italy; NOELL, Wu¨ rzburg, Germany), February, 1998. [6] ANSYS Release 5.5, ANSYS Inc., September 1998.
Structural analysis and verification of the ITER TF model coil test conditions S. Raff a,*, P. Schanz a, H. Fillunger b, B. Glaßl c a
Forschungszentrum Karlsruhe, Postfach 3640, D-76021 Karlsruhe, Germany b EFDA Close Support Unit, D-85748 Garching, Germany c Noell KRC, D-97076 Wu¨rzburg, Germany
Abstract An FE-model already used during the design of the test assembly consisting of the International Thermonuclear Experimental Reactor (ITER) Toroidal Field Model Coil (TFMC), the EURATOM LCT-coil and the Inter Coil Structure (ICS) was extended to allow for predictions of tests, which will be performed in the TOSKA facility. For the first test step, with the TFMC current loaded alone (single coil test), predictions are given for 80 kA, the design current. Because of some uncertainty in the friction behaviour between winding pack (WP) and coil case, a parameter study was performed describing the limiting cases of the coil behaviour. Since the mechanical sensors could be installed only on the outer coil case surface, the possibility of deriving from this information details of the internal coil behaviour also is discussed. © 2001 Elsevier Science B.V. All rights reserved. Keywords: FE-model; Inter Coil structure (ICS); Toroidal Field Model Coil (TFMC)
1. Introduction The TFMC which is under construction under the responsibility of the European Home Team will be tested in TOSKA, a facility for testing large superconducting magnets at Forschungszentrum Karlsruhe. Two steps are planned. First, the TFMC will be tested in its self field (single coil test) and afterwards in the background field of the European LCT-coil. In the past, the mechanical analysis concentrated on the design [1] and on the
* Corresponding author. Tel.: + 49-7247-82-3768; fax: + 49-7247-82-3718. E-mail address: [email protected] (S. Raff).
mechanical instrumentation [2,3]. Now, it is focussed on analysis for test preparation [4] and test predictions. For the test evaluation, the relatively simple single coil test is a favourite starting point since nearly no interferences with the other test rig components have to be expected, and the stress and deformations of the TFMC have some symmetries allowing certain sensor checks.
2. The finite element model To perform test predictions for the mechanical behaviour of the test assembly consisting of the two coils (TFMC and LCT-coil) and the ICS in between, a previous mechanical model developed
0920-3796/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 0 - 3 7 9 6 ( 0 1 ) 0 0 4 5 2 - 5
248
S. Raff et al. / Fusion Engineering and Design 58–59 (2001) 247–251
by industry [5] was extended to describe the electromagnetic as well as the mechanical behaviour. Using the ‘multi physics’ FE-code ANSYS [6], the same nodalization could be used for both subjects, reducing the computational effort for the investigation of different loading cases. The newly added electromagnetic model consists of the two winding packs (WP) of the TFMC and the LCT-coil, using geometry and grids from the mechanical model. The resulting Lorentz forces at the grid nodes are the load input for the mechanical model. To obtain a suitable mechanical model (Fig. 1), some modifications were done concerning the LCT-coil WP, the TFMC supporting in the ICS, the contact elements allowing for friction at all interfaces, introduction of final design modifications, the real supporting structure and additional connections between the coils.
Fig. 2. The electromagnetic model and resulting magnetic field for the single coil test (iTFMC =80 kA, iLCT =0 kA).
3. Results for the single coil test
Fig. 1. The mechanical model with the model coil (TFMC) fixed in the inter coil structure (ICS) and the LCT-coil behind.
To perform the single coil test, an analysis was performed for the maximum design current of 80 kA. The maximum magnetic field of 7.0 T occurring locally in the curved parts of the racetrack form (Fig. 2) differs slightly from the results of more sophisticated models [4]. However, the resulting Lorentz forces depend only weakly on such local peak values. The calculated force distribution, which is symmetric in out-of-plane direction for this load case, produces maximum stresses of 170 MPa (Tresca stress intensity) in the casing and about 100 MPa (tangential) in the WP, both in the curvature near the surface of the inner bore due to bending effects caused by the coil expansion. The maximum value of the interpancake shear stress of the WP is about 17 MPa. These values are about 40% of the values calculated for the double coil loading case calculated for the design [1]. For all former analyses [5], zero friction between WP and coil case was assumed. Now fric-
S. Raff et al. / Fusion Engineering and Design 58–59 (2001) 247–251
249
Table 1 Influence of friction between winding pack and casing on coil deformation; single coil test of TFMC, i= 80 kA Friction coefficient
Maximum coil expansion (mm)
Outer joint region elongation a (mm)
Winding pack m max tan (%)
Winding pack | max tan (MPa)
Casing | max Tresca (MPa)
Casing | max tan (MPa)
0.0 0.3 10.0
2.38 2.15 1.99
1.04 0.80 0.70
0.095 0.092 0.085
104 100 91
173 161 169
167 160 172
a
Measured length 1.50 m (part of straight back leg).
tion has been considered. But since the friction behaviour is not known very well so far, a parameter study was performed with the limiting cases of zero friction and bonding. In the analysis, the latter was approximated using a high friction coefficient of 10 (Coulomb friction approach). In addition, a somewhat realistic coefficient of 0.3 was used. Table 1 shows the influence of friction on the horizontal coil expansion, the maximum values of stress in the coil case, the tensile stress and strain in the WP and the outer joint region elongation of the WP. It should be mentioned that friction might reduce the joint region elongation, which is a critical quantity of the coil [1], by about 35% at maximum. With the exception of the casing stresses, all given quantities show a systematic correlation to friction.
back leg-part housing the joints; (b) Strain gauges (rosettes) to determine the coil stressing; (c) Strain gauges (uniaxial) to determine the deformation of the coil case walls at a horizontal and vertical cut. A few selected predictions for the sensor values are shown in Table 2 depending on the abovementioned friction coefficients. For some quantities in the table, a rather clear dependence on
4. Sensor predictions and derivable information Since it was not possible, due to safety reasons, to install mechanical instrumentation inside the coil, the coil behaviour can only be observed by displacement sensors and strain gauges mounted on the outer coil case surface. Therefore, one important question is whether the measured values on the coil case allow for a reliable determination of the internal coil behaviour, e.g. the internal WP behaviour and the above-mentioned friction effects. Fig. 3 shows the sensor types and locations on the TFMC case. There are three groups of measurements: (a) Displacement sensors to observe the global coil expansion under load (horizontal and vertical) and the elongation of the straight
Fig. 3. Mechanical sensors on the coil case: strain gauge rosettes (GRI), strain gauges uniaxial (GEI) and displacement devices (GDI).
S. Raff et al. / Fusion Engineering and Design 58–59 (2001) 247–251
250
Table 2 Predictions for some selected sensors; single coil test, i =80 kA Friction coefficient
0 0.3 10.0 a b
Dl
a
Dl
b
|Tresca
|y
GDI773 (mm)
GDI771 (mm)
GRI820 (MPa)
GRI826 (MPa)
GEI839 (MPa)
GEI838 (MPa)
0.45 0.50 0.60
−0.33 −0.31 −0.29
145 142 148
77 84 100
67 60 21
−20 −18 −14
Measured length 1.50 m (part of straight back leg outside). Measured length 1.24 m (part of straight back leg inside).
friction can be seen, for others not. The clue for that lies in the contact behaviour between WP and the casing. Fig. 4 shows a cross-section through the coil (top: undeformed; bottom: deformed). Under current load, the WP is pressed on the outer case wall (outer ring) along the whole circumference, but between WP and the inner case wall (inner ring), a gap opens decoupling the WP from the casing to some extent. The coupling on the outer ring depends on friction. Thus, the sensor values measured near or on the outer ring will depend more strongly on friction than the quantities on or near the inner ring of the coil case. Comparing, e.g. the predicted elongations of the case along the outer joint region given by sensor GDI773 (Table 2, column 2), the value clearly increases with increasing friction. This has to be compared with the values from Table 1 for the WP elongation (column 3). In the case of high friction, the values of both tables should approach each other. The highest WP elongation occurs without friction, whereas the coil case elongation shows a reciprocal behaviour. Due to the gap, this cannot be observed at the inner joint region. Nearly no-friction dependence shows the maximum case stresses (Table 1). The predicted values for the stress sensor GRI820 lie near the same location (inner edge of vertical coil cross-section) and show no dependence, too. But the values of sensor GRI826 (Table 2, column 5) lying near the outside edge in the horizontal cross-section again clearly depend on friction. The uniaxial stress values (sensors GEI838 and 839), observing the deformation behaviour of the inner and outer ring
wall behaviour, can also be explained by the gap formation combined with wall bending effects due to the WP pressed on the outer coil casing part. In principle, for the interpretation of the measurements, this local dependent behaviour may help to estimate the influence of friction. E.g., the quantities with weak dependence on friction will
Fig. 4. Cross-section of undeformed (top) and deformed (bottom) TFMC (deformation scaling factor =70).
S. Raff et al. / Fusion Engineering and Design 58–59 (2001) 247–251
allow to determine the stress level of the coil whereas the relation of ‘friction-dependent’ values to ‘friction-independent’ values may allow to draw some conclusions concerning the actual friction effects.
5. Conclusions Predictions for the single coil test of the TFMC have been gained performing electromagnetic and mechanical analysis with an improved and modified FE-model. A special item of the analysis was to estimate the influence of friction between WP and coil case in order to assess the stresses in the WP. A parameter study showed the influence on some quantities that characterize the coil behaviour. The task of the test evaluation concerning the mechanical sensors will be to determine, e.g. the influence of friction on the coil behaviour by sensor values gained solely on the outer coil surface. The evaluation of the predictions at the sensor positions showed that this may be possible to some extent. Thus, the single coil test results will help to analyze the more complex coil behaviour in the following TFMC test in the LCTcoil field.
251
References [1] P. Libeyre, B. Crepel, P. Decool, H. Fillunger, B. Glaßl, U. Hoeck, R. Kreutz, R. Maix, R. Meyer, R. Penco, S. Raff, E. Theisen, N. Valle, From conceptual to engineering design of the ITER TFMC, Proceedings of the 20th SOFT, Marseille, France, 7 – 11 September, 1998, pp. 767 – 770. [2] A. Ulbricht, M.S. Darweschsad, J.L. Duchateau, H. Fillunger, S. Fink, G. Friesinger, R. Heller, P. Hertout, P. Libeyre, G. No¨ ther, S. Raff, F. Wu¨ chner, G. Zahn, The preparations for testing the ITER Toroidal Field Model Coil (TFMC), Proceedings of the 20th SOFT, Marseille, France, 7 – 11 September, 1998, pp. 739 – 742. [3] H. Fillunger, F.H. Hurd, G. Zahn, A. Ulbricht, P. Libeyre, E. Theisen, F. Beaudet, ITER TF Coil assembly, commissioning and instrumentation, Proceedings of the 21st SOFT, Madrid, Spain, 11 – 15 September, 2000. [4] J.L. Duchateau, H. Fillunger, S. Fink, R. Heller, P. Hertout, P. Libeyre, R. Maix, C. Marinucci, A. Martinez, R. Meyder, S. Nicollet, S. Raff, M. Ricci, L. Savoldi, A. Ulbricht, F. Wuechner, G. Zahn, R. Zanino, Test program preparations of the ITER toroidal field model coil (TFMC), Proceedings of the 21st SOFT, Madrid, Spain, 11 – 15 September, 2000. [5] B. Glaßl, Stress analysis of the inter coil structure ICS by a 3D FE programme, AGAN technical report TR-NO-004, Consortium AGAN (ACCEL, Bensberg, Germany; ALSTOM, Belfort, France; ANSALDO, Genova, Italy; NOELL, Wu¨ rzburg, Germany), February, 1998. [6] ANSYS Release 5.5, ANSYS Inc., September 1998.