2019 Vol.9(3)


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Mechanics of Tokamak fusion components
Theoretical and Applied Mechanics Letters  2019, 9(3): 145-146. doi: 10.1016/j.taml.2019.03.016
[Abstract](653) [FullText HTML] (332) [PDF 4609KB](28)
Delamination strength of HTS tape under transverse tensile stress and its enhancement by using different Ag layer depositing temperatures
Jun Wang, Ce Sun, Liu Cong, Xingyi Zhang, Youhe Zhou
Theoretical and Applied Mechanics Letters  2019, 9(3): 147-151. doi: 10.1016/j.taml.2019.03.002
[Abstract](758) [FullText HTML] (346) [PDF 2666KB](21)
For the application of second generation high temperature superconducting coated conductors (CCs) with layered structures, thermal mismatch between different components and electro-magnetic force exerted in superconducting layer in a working magnet can cause transverse tensile stress, which would result in delamination behavior. Therefore many research groups have designed experiments to measure the delamination strength and dedicate to improving that. However, the reason of the discrete distribution of measured data has still not get quantitatively studied, besides, there are lack of investigations on the method of changing depositing conditions to improve the delamination strength except by adding an additional metal layer. In this work, we adopt an anvil test device and obtain delamination strengths as 29.6 MPa of YBa2Cu3O7−x (YBCO)/buffer and 114.6 MPa of buffer/substrate by combing energy disperse spectroscopy (EDS) detection. The reason of discretized measurement data on the delamination strength is explained. Moreover, we find that different temperatures during Ag deposition determine the bonding force of Ag and YBCO layer. The Delamination strength between Ag and YBCO layer increases from 4.4 MPa to larger than 114.6 MPa with temperature elevated from 30 °C to 100 °C. Hence we present a novel method for improving the delamination strength of YBCO CCs by setting an optimal temperature of Ag deposition.
Numerical study of MHD mixed convection under volumetric heat source in vertical square duct with wall effects
Zhi-Hong Liu, Ming-Jiu Ni, Nian-Mei Zhang
Theoretical and Applied Mechanics Letters  2019, 9(3): 152-160. doi: 10.1016/j.taml.2019.03.008
[Abstract](707) [FullText HTML] (330) [PDF 3245KB](18)
Magnetohydrodynamic (MHD) mixed convection under strong magnetic field and volumetric heat source for buoyancy-assisted flows are studied numerically in this paper. Blanket is one of key components for energy conversion in Tokamak fusion reactor. The physical model employed for simulations is refined from dual-coolant lead-lithium (DCLL) blanket. A magnetic-convection code based on a consistent and conservative scheme is developed with the help of finite volume method, and validated by some Benchmark analytical solutions. The flows inside duct with thermal insulating and electric conducting walls under exponential neutron volumetric heat source are simulated. Based on Boussinesq assumption, the influences of wall electrical conductivity and buoyancy on velocity fields, temperature distributions and Nusselt numbers are investigated. Results illustrates that the wall conductance ratio dominates the flow at low Grashof numbers and high wall conductance ratio, while buoyancy effect dominates the jet flow near side wall at a high Grashof number. In addition, the velocity along flow direction substantially impacts features of the Nusselt number and temperature distribution. Besides, the jet flow results in a higher Nusselt number and lower temperature.
Progress on design and related R&D activities for the water-cooled breeder blanket for CFETR
Songlin Liu, Xiaoman Cheng, Xuebin Ma, Lei Chen, Kecheng Jiang, Xia Li, Hui Bao, Jichao Wang, Wanjing Wang, Changhong Peng, Peng Lu, Min Li, Kai Huang
Theoretical and Applied Mechanics Letters  2019, 9(3): 161-172. doi: 10.1016/j.taml.2019.03.001
[Abstract](935) [FullText HTML] (465) [PDF 3586KB](23)
The water-cooled ceramic breeder (WCCB) blanket is one of the blanket candidates for Chinese fusion engineering testing reactor (CFETR) and is being developed at the Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP). This paper reviews design and evolution of the WCCB blanket for CFETR, and presents a new WCCB blanket design according to the latest CFETR core parameters (major and minor radii are R = 7.2 m and a = 2.2 m, respectively) and missions. This new design is expected to satisfy multiple CFETR operation modes of 0.2, 0.5, 1.0, and 1.5 GW fusion power and achieve tritium self-sufficiency. The feasibility of the updated blanket design is evaluated from the aspects of neutronics and thermo-hydraulics. Furthermore, the research and development (R&D) activities supporting to the WCCB blanket for CFETR are reported, including the design code, the water loop experiments, the pebble bed modeling and experiments, and the components fabrication technology.
Numerical methods for the magneto-mechanical coupling analysis of in-vessel components in Tokamak devices
Xudong Li, Shejuan Xie, Cuixiang Pei, Zhenmao Chen
Theoretical and Applied Mechanics Letters  2019, 9(3): 173-179. doi: 10.1016/j.taml.2019.03.009
[Abstract](873) [FullText HTML] (356) [PDF 2948KB](19)
Magneto-mechanical coupling vibration arises in the in-vessel components of Tokamak devices especially during the plasma disruption. Strong electromagnetic forces cause the structures to vibrate while the motion in turn changes the distribution of the electromagnetic field. To ensure the Tokamak devices operating in a designed state, numerical analysis on the coupling vibration is of great importance. This paper introduces two numerical methods for the magneto-mechanical coupling problems. The coupling term of velocity and magnetic flux density is manipulated in both Eulerian and Lagrangian description, which brings much simplification in numerical implementation. Corresponding numerical codes have been developed and applied to the dynamic simulation of a test module in J-TEXT and the vacuum vessel of HL-2M during plasma disruptions. The results reveal the evident influence of the magnetic stiffness and magnetic damping effects on the vibration behavior of the in-vessel structures. Finally, to deal with the halo current injection problem, a numerical scheme is described and validated which can simulate the distribution of the halo current without complicated manipulations.
Progress on the ultrasonic testing and laser thermography techniques for NDT of tokamak plasma-facing components
Cuixiang Pei, Haochen Liu, Jinxing Qiu, Tianhao Liu, Zhenmao Chen
Theoretical and Applied Mechanics Letters  2019, 9(3): 180-187. doi: 10.1016/j.taml.2019.03.011
[Abstract](1024) [FullText HTML] (393) [PDF 3012KB](23)
During manufacturing and operation, different kinds of defects, e.g., delamination or surface cracks, may be generated in the plasma-facing components (PFCs) of a Tokamak device. To ensure the safety of the PFCs, various kinds of nondestructive testing (NDT) techniques are needed for different defect and failure mode. This paper gives a review of the recently developed ultrasonic testing (UT) and laser thermography methods for inspection of the delamination and surface cracks in PFCs. For monoblock W/Cu PFCs of divertor, the bonding quality at both W-Cu and Cu-CuCrZr interfaces was qualified by using UT with a focus probe during manufacturing. A non-contact, coupling-free and flexible ultrasonic scanning testing system with use of an electromagnetic acoustic transducer and a robotic inspection manipulator was introduced then for the in-vessel inspection of delamination defect in first wall (FW). A laser infrared thermography testing method is highlighted for the on-line inspection of delamination defect in FW through the vacuum vessel window of the Tokamak reactor. Finally, a new laser spot thermography method using laser spot array source was described for the online inspection of the surface cracks in FW.
Considering for the blanket structure scheme of HCCB DEMO
Zhou Zhao, Zaixin Li, Xiaoyu Wang, Xueren Wang, Kaiming Feng
Theoretical and Applied Mechanics Letters  2019, 9(3): 188-194. doi: 10.1016/j.taml.2019.03.013
[Abstract](661) [FullText HTML] (371) [PDF 3014KB](18)
For the solid blanket concept of helium cooled ceramic breeder (HCCB) demonstration fusion power plant (DEMO), a feasible blanket structure with configuration 2×X is proposed as considering relatively low temperature limit of neutron multiplier beryllium pebbles. Based on that, preliminary design for the typical blanket module of HCCB DEMO has been carried out and verified by thermal-hydraulic analysis and structural analysis. Furthermore, the specific relationship of maximum temperature depended on the surface heating of blanket key part first wall (FW) is also analyzed.
Heat transfer performance for DCLL blanket with no-wetting insulator walls
Hulin Huang, Shimou Yin, Guiping Zhu
Theoretical and Applied Mechanics Letters  2019, 9(3): 195-201. doi: 10.1016/j.taml.2019.03.003
[Abstract](741) [FullText HTML] (345) [PDF 3083KB](9)
Magnetohydrodynamic (MHD) effect and heat transfer are two key issues for design of dual coolant lead lithium (DCLL) blanket. Flow channel insert (FCI) has been applied to decouple the liquid metal from the walls to efficiently decline MHD pressure drops and reduce heat losses from the liquid metal for increasing bulk exit temperatures of the blanket. However, there are still big pressure drops and a higher velocity jet located at the gap flow. Moreover, the FCI made from silicon carbide (SiC) constitutes a complex blanket structures which potentially causes special flow phenomena. In the present work, the characteristics of fluid flow and heat transfer in the DCLL blanket channel are investigated for the first wall (FW) sprayed a layer of no-wetting nano coating (NWNC) on its inner surface. The results show that the pressure drop with NWNC wall is one-order magnitude lower than that with FCI in the general DCLL blanket. The Nusselt number on the NWNC wall is about half of that on the general wall. On this basis, a heat transfer criterion equation of DCLL channel is achieved for the NWNC wall without FCI. The results are compared with that criterion equation of general wall conditions, which indicates the criterion equation can well predict the convection heat transfer of DCLL channel.
Numerical simulation of droplet-formation in rotary atomizer
Naoki Igari, Takuro Iso, Yu Nishio, Seiichiro Izawa, Yu Fukunishi
Theoretical and Applied Mechanics Letters  2019, 9(3): 202-205. doi: 10.1016/j.taml.2019.03.015
[Abstract](738) [FullText HTML] (348) [PDF 2652KB](23)
Numerical simulations of the liquid flow scattering from rotary atomizers are performed using an incompressible smoothed particle hydrodynamics (SPH) method. The influence of grooves at the edges of the atomizers on the formation of ligaments and droplets is investigated changing the numbers and shapes of the grooves. As a result, it is found that small droplets are likely to be generated when the number of grooves is large and the depth of grooves is deep. It is also found that the grooves work more effectively in bell-cup atomizers than in disk type atomizers.
Torsional negative stiffness mechanism by thin strips
Jinyou Li, Kangjia Fu, Yongpeng Gu, Zhihua Zhao
Theoretical and Applied Mechanics Letters  2019, 9(3): 206-211. doi: 10.1016/j.taml.2019.01.012
[Abstract](971) [FullText HTML] (498) [PDF 4114KB](38)
Negative stiffness mechanisms have great application potential in different fields, such as vibration isolation, energy absorption and mesh antenna unfolding. Although numerous compliant mechanisms with negative stiffness features have been implemented in literature, the designing work remains in its infancy, and proposing an original design strategy may open a new avenue for the future inventions. In this study, inspired by a toy, we developed a novel type of compliant mechanism composed of thin strips, possessing negative stiffness property under torsion. The negative stiffness feature is achieved by large deformation of the strips rather than mechanical buckling. As a consequence, the obtained negative stiffness segment covers a significantly long range. Demonstrated with examples, it was shown that the proposed mechanisms could be combined with other compliant mechanisms to realize long-range unusual torque-angle relationships, which can be used in different applications.
Preferential orientation of tracer spheroids in turbulent channel flow
Yucheng Jie, Lihao Zhao, Chunxiao Xu, Helge I. Andersson
Theoretical and Applied Mechanics Letters  2019, 9(3): 212-214. doi: 10.1016/j.taml.2019.03.010
[Abstract](642) [FullText HTML] (340) [PDF 2465KB](24)
Axis-symmetric spheroids, such as rod-like and disk-like particles, have been found to orient preferentially in near-wall turbulence by both experiment and numerical simulation. In current work we examined the orientation of inertialess spheroids in a turbulent channel flow at medium friction Reynolds number \begin{document}${{{ Re}} _{\rm{\tau }}} = 1000$\end{document} given based on the half of channel height. Both elongated prolate spheroid and flat oblate spheroid are considered and further compared with the reference case of spherical particle. The statistical results show that in near wall region the prolate spheroids tend to align in the streamwise direction while the oblate spheroids prefer to orient in the wall-normal direction, which are consistent with earlier observation in low Reynolds number (\begin{document}${{{ Re}\nolimits} _{\rm{\tau }}} = 180$\end{document}) wall turbulence. Around the channel center we found that the orientation of spheroids is not fully isotropic, even though the fluid vorticity are almost isotropic. The mechanism that gives rise to such particle orientations in wall-turbulence has been found to be related to fluid Lagrangian stretching and compression (Zhao and Andersson 2016). Therefore, we computed the left Cauchy-Green strain tensor along Lagrangian trajectories of tracer spheroids in current flow field and analyzed the fluid Lagrangian stretching and compression. The results indicated that, similar to the earlier observations, the directions of the Lagrangian stretching and compression in near-wall region are in the streamwise and wall-normal directions, respectively. Furthermore, cross over the channel the prolate spheroids aligned with the direction of Lagrangian stretching but oblate spheroids oriented with the direction of Lagrangian compression. The weak anisotropy of orientations of fluid Lagrangian stretching and compression observed at the channel center could be the reason for the aforementioned modest anisotropic orientation of spheroids in channel central region.