| With the rapid development of large scale scientific construction project,new energy,modern medicine and transportation fields,the researches on the theory and application of superconducting magnets are developing towards the direction of high magnetic field and high loading current.It will bring revolutionary technological advancement and breakthrough in the furture.Under the complicated multi-field,the high-field superconducting magnets carrying with high current density are commonly exposed to large Lorentz forces,which leading to the unavoidable deformation in superconducting coils.The coupling behaviors of multi-field interaction also have the significant influence on the properties of superconducting magnets,even further disturb the magnetic field quality and the operating safety and stability of the superconducting magnets.Therefore,in the process of the development and stable operation of large-scale and high-field superconducting magnets,the issues of the mechanics and the multi-field coupling will be challenging research topics with cutting-edge multi-disciplinary crossing area.Currently,the development and design of the large-scale and high-field superconducting magnets are still in the exploratory stage.The related researches in the world are still far from meeting the application requirements of supercongducting magnets with higher and higher demands on their performance.From the structural design to the operation of superconducting magnets under extreme multi-field,they are all involved the experimental characterization of mechanics and multi-field coupling behavious,and the effective analysis method with high precision.In the experimental aspect,the mechanics and multi-field measurements of superconducting magnets in extreme operating environments face some challenges of the invalidation of conventional measuring methods.In aspect of numerical simulations,it is often difficult to effectively characterize the multi-field and multi-scale characteristics of superconducting composite magnets by using the traditional analysis methods and the homogenization approaches of superconducting composite magnets.Therefore,based on the non-electromagnetic measurement technique,for example,fiber Bragg gratings strain sensing technology,and the micromechanical theory of superconducting coil,the experimental characterization of mechanical properties and the numerical analysis of magneto-mechanical coupling of superconducting composite magnets were studied under extremely complex multi-field in this dissertation.The results of experiment and numerical simulation were compared and analyzed,to reveal the multi-field performance and coupling behavior of superconducting composite magnets.In this dissertation,the magneto-mechanical behaviors of a superconducting solenoid magnet and a racetrack superconducting magnet under extremely complex multi-field environment are systematically studied.The main research contents and results are as follows.(1)The non-electromagnetic measurement technique,fiber Bragg gratings strain sensing technology,was extended to the experimental measurement of superconducting magnets under extreme operating environments.A soft substrate-polyimide coated fiber Bragg gratings was designed and fabricated to apply to the embedded strain measurement of superconducting magnets in the ultra-low temperature and high magnetic field.Additionally,the experimental calibration was carried out in low/variable temperature environment,the results showed that the strain sensitivity coefficient of the soft substrate-polyimide coated fiber Bragg gratings is independent of temperature in the ultra-low temperature region,and its performance is much stable.(2)A new method of strain measurement of superconducting composite magnet based on the embedded soft substrate-polyimide coated fiber Bragg gratings was established.And the experimental studies for the mechanical deformation of the superconducting solenoid magnet and racetrack superconducting magnet are also carried out.The experimental result showed that the soft substrate-polyimide coated fiber Bragg gratings is superior to the cryogenic resistance strain gauge for the embedded strain measurement and monitoring of superconducting composite magnet,especially for the multi-point embedded strain measurement and monitoring.Additionally,the result also showed that the embedded soft substrate-polyimide coated fiber Bragg gratings can achieve the high-precision strain measurement and real-time strain monitoring inside the superconducting magnet structure,and its strain measurement has good stability and accuracy.(3)The magneto-mechanical coupling finite element model was established based on the homogenization method of macroscopic isotropy of superconducting composite coils.The isotropic homogenized model(IHM)is used to numerically simulate and analyze the magneto-mechanical behaviours of the superconducting solenoid magnet and the racetrack superconducting magnet,and compared with the experimental results.The results showed that the prediction results of the magneto-mechanical coupling finite element model are in better agreement with the experimental results than the results of the finite element model without considering the magneto-mechanical coupling effect.The magneto-mechanical coupling effect becomes more significant with the increase of excitation current and magnetic field,it can not be ignored in the design and analysis of superconducting magnet.(4)In order to more accurately analyze the multi-field behavior of the superconducting solenoid magnet and racetrack superconducting magnet,the orthotropic multi-scale finite element model(OHM)and the detailed hierarchical multi-scale finite element model(DHM)were established based on the theory of composite micro-mechanics and the microstructure of superconducting composite coils and superconducting composite wires.The results showed that the numerical results by the OHM and the DHM agree well with the experiment measurements on strain,the predicted results by the IHM always are quite deviation from the measurements,especially at high magnetic field.Additionally,the DHM can exhibit more details of mechanical characteristics inside superconducting composite coils,such as the superconducting composite wires,insulation layers and filling material regions.These results will provide a helpful theoretical basis for the design of superconducting magnets.Through these studies,we preliminarily realized the embedded strain measurement and the characterization of multi-field behaviors of superconducting composite magnet,and especially in the effective and detailed analysis of the magneto-mechanical coupling behavior of superconducting composite magnet.These research methods and results may provide the useful guidances and multi-field quantitative analysis framework for the design,development and operation test of the superconducting magnet with high field. |
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