372 Ë 10 HTS Maglev launch technology
A numerical method to evaluate the levitation force relaxation under load based
on the current vector potential (T) method was introduced (see Section 7.6.2), which
could reveal visually the configuration and distribution of supercurrent within a
HTS bulk. The simulation results showed nearly the same trend as the experimental
results, which was helpful in the qualitative analyses of levitation characteristics. The
calculation could display the influence of the load on the current density distribution
clearly. From these results, it was found that the zone of current density< 1 × 107 A/m^2
decreased with the load increase; in other words, the shielding currents in the HTS
bulk increased with the load increase.
The influence of the vertical inclination of the PMG on the levitation characte-
ristics of HTS Maglev systems was investigated [13, 14]. To investigate the influence
of the angle of vertical inclination, a HTS Maglev launch platform was designed and
fabricated. The levitation forces, guidance, and driving forces were tested over the
inclined angle range of 0∘to 18∘.
The experimental results indicated that the levitation gap increased with the
increase in the incline angle. However, the levitation forces of HTS bulks and the
driving forces of the linear motor decreased with the increase in vertical angle. When
the vertical incline angle increased from 0∘to 18∘, the levitation gap increased 0.65 mm
and the levitation forces decreased 10% [14]. The guidance forces were not influenced
by the change in the levitation gap.
Furthermore, the influence of the transverse slope of the PMG on the HTS Maglev
system was also investigated [15]. The experiments on transverse slope were tested by
the SCML-1 system (see Section 5.3) with a specially designed measurement platform.
The levitation and guidance forces of HTS bulks for transverse angles from 0∘to 12∘
were tested. The results showed that the levitation and guidance forces increased and
decreased with the increase in the transverse slope, respectively.
The dynamic response of HTS bulks above the PMG was very important to the
practical application of the HTS Maglev launch system, especially under high-speed
operation. The dynamic stiffness, the displacement and the levitation forces of the
HTS bulks were measured under external vibration with excitation amplitudes of
1–4 mm and frequencies of 1–400 Hz [16]. The experimental results indicated that
the levitation forces, the resonance frequency and the dynamic stiffness of the HTS
bulks decreased with the increase of excitation amplitude, under the conditions
of excitation frequency<30 Hz and excitation amplitude>3 mm. The influence of
excitation frequency on the levitation performance of HTS bulks was weak, with
exception of resonant frequencies. The energy loss due to vibration was the main
reason that caused attenuation of levitation performance. Furthermore, the expe-
rimental results also showed that the serious reduction in levitation performan-
ce occurred mainly in the first several cycles of vibration, which meant that the
HTS bulks could sustain external vibration in the vertical direction and recover
to a new balance point, due to their strong flux pinning ability and levitation
stiffness.