Magneto-Thermal Thin Shell Approximation for 3D Finite Element Analysis of No-Insulation Coils

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A new module, Pancake3D, of the open-source Finite Element Quench Simulator (FiQuS) has been developed in order to perform transient simulations of no-insulation (NI) high-temperature superconducting (HTS) pancake coils in 3-dimensions. FiQuS/Pancake3D can perform magnetodynamic or coupled magneto-thermal simulations. Thanks to the use of thin shell approximations, an H-Φ formulation, and anisotropic homogenization techniques, each turn can be resolved on the mesh level in an efficient and robust manner. FiQuS/Pancake3D relies on pre-formulated finite-element (FE) formulations and numerical approaches that are programmatically adjusted based on a text input file. In this paper, the functionalities and capabilities of FiQuS/Pancake3D are presented. The challenges of FE simulation of NI coils and how FiQuS/Pancake3D addresses them are explained. To highlight the functionalities, the results of a magneto-thermal analysis of a double pancake coil with 40 turns per pancake with local degradation of the critical current density are conducted and discussed. Furthermore, a parameter sweep of the size of this local degradation is presented. All the FiQuS input files for reproducing the simulations are provided.

An open-source 3D FE quench simulation tool for no-insulation HTS pancake coils

Atalay,

Schnaubelt,

Wozniak

et al. 2024

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Modeling of contact resistivity and simplification of 3D homogenization strategy for the H formulation

Wang,

Yong,

Zhou

2024

The finite element method (FEM) provides a powerful support for the calculations of superconducting electromagnetic responses. It enables the analysis of large-scale high-temperature superconducting (HTS) systems by the popular H formulation. Nonetheless, modeling of contact resistivity in three-dimensional (3D) FEM is still a matter of interest. The difficulty stems from the large aspect ratio of the contact layer in numerical modeling. Nowadays, an available solution is to model the contact layer with zero thickness but requires the discontinuity conditions of the magnetic field. In this paper, the energy variational method is utilized to incorporate the contribution of contact resistivity into the H formulation. From the perspective of energy transfer, the contact resistivity is related to the energy dissipation of the radial current flowing through the contact interface. In terms of applications, this method can be employed to calculate the charging delay of no-insulation (NI) coils and the current sharing behaviors of CORC cables. One advantage of this model is that the magnetic field is continuous and hence can be easily implemented in FEM. Additionally, it requires fewer degrees of freedom and hence presents advantages in computational efficiency. Moreover, this method can be employed to simplify the 3D H homogeneous model for insulated coils. The above discussions demonstrate that the proposed model is a promising tool for the modeling of contact resistivity.

Fast and accurate 3D FEM model for electromagnetic simulations of no-insulation HTS coils based on polygon-anisotropic-resistivity

Zhong,

Wu,

Jin

2024

For no-insulation (NI) high-temperature superconducting (HTS) coils, a 3D electromagnetic model, which is fast and accurate, conducive to establish, and straightforward to muti-physics coupling, is still required. This paper introduces a polygon-anisotropic-resistivity (PAR) method for 3D FEM electromagnetic simulations of NI HTS coils. This model avoids dividing each tape into the specific HTS-tape layer and turn-to-turn contact layer, which yields: (1) a reduced computational burden; (2) improved convergence due to smaller element aspect ratios. The significance of the polygon-anisotropic-resistivity method lies in its indispensable role in achieving a 3D anisotropic-resistivity model with high computing speed and accuracy. The proposed PAR model is rigorously evaluated through three types of simulations: (1) charge and discharge tests; (2) AC losses of the NI coil subjected to AC fields with a DC current supply; (3) heat-triggered quench and recovery scenarios. For these simulations, the PAR model is validated by comparisons with the full-element model, namely, the 3D FEM model that explicitly incorporates each specific HTS-tape layer and turn-to-turn contact layer in the H-formulation model. Good consistency is observed. The computing speed of the PAR model is tested to be 12-38 times that of the full-element model with the same accuracy. The PAR model achieves a 40 % reduction in degrees of freedom compared to the full-element model, with the same mesh density along the HTS tape width and length, facilitating more precise and larger scale coil simulations within the same computational memory limits. Additionally, the PAR model entirely eliminates the inherent inaccuracies found in the conventional-anisotropic-resistivity 3D model, which stem from discrepancies between the arranged anisotropic-resistivity and the actual computed coil meshes. The proposed PAR model will enhance the prevalence of 3D electromagnetic analyses of NI HTS coils.