High Temperature Superconducting Maglev Research Articles

Enhancing dynamic stability of HTS maglev systems with preloading method

High temperature superconducting (HTS) bulks have strong flux pinning capabilities and are widely used in various fields. Their self-stabilizing characteristics also provide new ideas for ultra-high-speed rail transit. For HTS maglev systems, operational stability, curve negotiation and safety when subjected to external forces are very important. Due to the hysteresis effect of superconducting bulks, they do not always return to their initial positions after deviating from the levitated position in an alternative external magnetic field. In some cases, the levitation system can be destroyed. Studies have shown that preloading can enhance quasi-static levitation performance. Therefore, this paper conducts a detailed analysis of the quasi-static levitation and guidance forces of HTS bulks above a Halbach permanent magnet guideway (PMG) under conditions with and without preloading. Additionally, the dynamic responses of the HTS bulks under lateral or vertical pulsed excitations are studied, with a particular focus on the final equilibrium position offset after disturbance. The results indicate that preloading can suppress the attenuation of the levitation force, enhance the guidance performance, and raise stiffness in both lateral and vertical directions. It also effectively suppresses position deviation from disturbance and increases the maximum excitation force threshold for system instability. This study provides practical insights for HTS maglev applications.

Modeling and dynamic performance of distributed force in high-temperature superconducting pinning magnetic levitation

High-temperature superconducting (HTS) pinning magnetic levitation (maglev) systems are highly promising for future applications in rail transportation. Through the interaction between onboard HTS bulks and the permanent magnet guideway (PMG), this system generates levitation and guidance forces, known as the HTS-PMG relationship. Under practical conditions, this interaction manifests itself as a distributed force. However, past models have only considered concentrated forces. This study aims to design experiments to investigate the HTS-PMG relationship and propose a more realistic discretized lateral-vertical coupling HTS-PMG relationship to accurately reflect torques in dynamic simulations. Based on this, a dynamic model is established to analyze the Sperling index and the five-degree-of-freedom dynamic response of the HTS pinning maglev vehicle system under different HTS-PMG relationship models. The results indicate that the proposed discretized lateral-vertical coupling HTS-PMG relationship accurately characterizes the torque generated by the HTS levitator, influencing lateral, roll, pitch, and yaw motions to some extent. Compared with the concentrated force model, the discrete force model exhibits superior dynamic performance, particularly in terms of lateral dynamics and the lateral Sperling index. This study provides valuable insights into the field of HTS maglev, particularly regarding investigating HTS-PMG relationships and their impact on HTS maglev system dynamic performance.

Design and test of a contactless damper for HTS maglev systems via electromagnetic shunt dampers

High-temperature superconducting (HTS) maglev system is promising to become the future high-speed transport due to its numerous advantages. However, the low-damping dynamic characteristics of superconductors make the system vulnerable to external disturbances, which present a significant challenge to its implementation. To enhance the vibration attenuation effect of the HTS maglev system, a non-contact damper that employs electromagnetic shunt damping (EMSD) and negative resistance is incorporated into the HTS maglev system. This study elucidates the principles of EMSD and negative resistance, and establishes the governing equations to describe the behavior of the HTS maglev model equipped with EMSD. Subsequently, the EMSD coupling coefficients are analysed via the finite element method (FEM) under varying conditions. Finally, a dedicated vibration test rig is designed and fabricated to validate the effectiveness of the proposed damper. The results demonstrate that the proposed damper, in combination with negative resistance, is capable of effectively suppressing vibration in HTS maglev systems. The maximum acceleration of the test model can be reduced by 86% compared with the original system without the damper. This work may provide valuable guidance for future practical implementations.

Optimization of Nd-Fe-B permanent magnet guideways with high-temperature stability

High-temperature superconducting (HTS) pinning Maglev systems are advantageous due to their ability to achieve large-scale passive-stabilized levitation. Elevated temperatures can lead to a reduction in the magnetic characteristics of the permanent magnet guideway (PMG), which may pose a risk to the safe functioning of HTS Maglev trains. In order to guarantee the secure and dependable functioning of HTS Maglev trains, it is necessary to augment the high-temperature stability of the PMG. This study involves simulating the high-temperature stability of present PMGs and developing a new PMG that exhibits greater performance. Magnetic field simulation is employed to compute the demagnetization of permanent magnets (PMs) in several typical PMGs, encompassing both reversible and irreversible scenarios, in order to examine the factors contributing to demagnetization and evaluate the thermal stability of the PMGs at elevated temperatures. The grade, size, and magnetization direction of the Halbach-type PMG are subsequently optimized and compared to the original Halbach-type PMG. Following this, ideas for further optimization are provided. The optimized Halbach-type PMG reduces the overall decay ratio of the highest magnetic flux density Bz by 5.77% compared to the existing Halbach-type PMG. Additionally, the irreversible decay ratio is decreased by 6.13% at 85 ℃. The levitation force decay ratio on the HTS bulks above the optimized Halbach-type PMG is decreased by 8.11% compared to the existing Halbach-type PMG. Additionally, the irreversible decay ratio is reduced by 9% at 85 ℃. This study provides valuable insights for enhancing the efficiency and performance of PMGs and HTS Maglev trains over extended periods of operation.

Measurement of levitation force of high-temperature superconducting maglev under high-speed operation condition

High-temperature superconducting (HTS) pinning magnetic levitation (maglev) has garnered significant attention in high-speed maglev transportation due to its inherent self-stability, low energy consumption, and absence of mechanical friction. Ensuring the safe and stable operation of HTS pinning maglev systems necessitates a dedicated focus on the performance and stability of HTS bulks levitated above the permanent magnetic guideway (PMG). Previous research has indicated that variations in the temperature within the HTS bulk can impact the levitation performance of the system. This temperature-related phenomenon occurs when the external magnetic field applied to the HTS bulk changes. However, it is noteworthy that previous levitation force tests for HTS magnetic levitation systems have been limited to quasi-static or low-speed studies. The exploration of dynamic levitation forces, particularly at high speeds, has remained constrained due to the associated high costs. Therefore, the objective of this study is to investigate dynamic levitation forces while the HTS pinning maglev system is in motion at high speeds, utilizing a self-developed ultra-high-speed maglev test rig. Initially, the relationship between the levitation force and the vertical displacement of the HTS pinning maglev system is examined based on quasi-static experiments. Subsequently, comparative studies are conducted to measure levitation forces at varying speeds. Finally, the correlation between running speed and dynamic levitation force is discussed. The investigation reveals that the levitation force experiences only a marginal decrease as the running speed increases. At a running speed of 240 km/h, the attenuation rate of the levitation force is approximately 2.478 %, demonstrating the commendable stability of HTS pinning maglev systems. The article concludes by presenting the dynamic levitation characteristics and their attenuation trends to speed. These findings can serve as valuable references for future design and practical implementation of HTS pinning maglev systems.

Thermal-vibration correlation study for high-temperature superconducting maglev intelligent monitoring based on back propagation neural network analysis

The internal temperature rise inside the high-temperature superconducting (HTS) superconductor (SC) resulting from irregular magnetic field (MF) above the permanent magnet guideway is a major factor contributing to the decline of levitation performance. Real-time monitoring of the temperature rise inside YBCO SC is an important issue for the safe operation of the maglev train systems. However, the existing temperature rise testing method involves destructive intrusion less or more, easily affected by strong MF, occupying limited space and sensors prone to detachment. This paper innovatively proposes a non-contact internal temperature rise testing method combining artificial intelligence (AI) methods. Vibration is common signal of a maglev train system, which inspires to establish a fundamental thermal-dynamic levitation force synchronous testing device for YBCO SC. Then, a set of temperature rise-vibration dataset exposed to different alternating MF frequencies is created. The wavelet transform is chosen to extract the frequency band energy of vibration, and the backpropagation neural network is used to identify the corresponding temperature rise. The recognition accuracy can reach over 99.9%, which firstly proves the effectiveness of AI algorithms in the thermal-vibration correlation analysis for the HTS maglev system. The results can provide the foundation reference for the intelligent monitoring and fault diagnosis of thermal-dynamics stabilities of HTS maglev train in the future.

Levitation performance evolution of high-temperature superconducting maglev vehicle under electromagnetism-heat-force strong coupling

ABSTRACT High-temperature superconducting (HTS) maglev is considered suitable for high-speed maglev systems because of its self-stability characteristic. However, when the HTS maglev vehicle vibrates, alternating current loss occurs in the onboard superconductor due to the change in the external magnetic field. It leads to the decrease of vehicle levitation height and seriously affects the safe and stable operation of the vehicle. So, in this paper, the levitation performance evolution of HTS maglev vehicle under the electromagnetism-heat-force strong coupling model is studied. The parameter of the air spring is optimized according to the ride index and levitation height decay. The effects of random irregularity at different speeds on vehicle levitation performance are compared. The influence of periodicity geometric irregularity on the levitation performance and ride comfort of HTS maglev vehicle are studied. This paper can provide data reference for the HTS maglev vehicle system in future engineering applications.

The effect of the modelling approaches in the assessment of comfort and curve negotiation performance of a small-scale maglev vehicle

In this article, a new co-simulation method was presented for high-temperature superconducting (HTS) magnetic levitation (Maglev) systems by utilizing H-formulation that is implemented in COMSOL Multiphysics®. A comparative study was conducted to evaluate the curve negotiation performance, which is closely related to its stability, of the HTS maglev vehicle running on a multi-surface permanent magnet guideway (PMG). Also, Sperling’s ride index method was used to evaluate ride comfort. Different from the existing related models of this subject, the dynamics of free-falling were incorporated into the modelling approach to simulate the actual running conditions of the vehicle. In addition, because of considering the non-stationary dynamics of the induced supercurrent in the HTS domain, the proposed approach and the selected route design provide simulation results that are close to the actual application of the HTS maglev vehicle. The results show that the performance indicators of the co-simulation greatly deviate from those of the existing curve-fitting-based models with increasing velocity.

Machine learning driven optimization and parameter selection of multi-surface HTS Maglev

This research aims to tackle the challenges posed by precise force measurement for high temperature superconducting (HTS) Maglev systems, including mechanical constraints, step motor limitations, and sensor resolutions. For this aim, six machine learning (ML) models namely Support Vector Machine (SVM), Gaussian Process Regression (GPR), Extreme Gradient Boosting (XGB), Long Short-Term Memory (LSTM), Extreme Machine Learning (EML), and Convolutional Neural Network (CNN) were developed to predict levitation force (Fz) and lateral force (Fx) based on process parameters including permanent magnet width (PMW), field cooling height (FCH), the movement in the z-axis (vertical distance), and the movement in the x-axis (lateral distance). Among six ML models, CNN emerged as the most accurate model, demonstrating smaller root mean square deviation (RMSD) without compromising correlation coefficients. Furthermore, an innovative process window approach was introduced to select process parameters that simultaneously meet the minimum value of Fz and maximum value of Fx, named β1 and β2, set at 90 N and 0 N, respectively. Within this window, PMW of 30 mm and z values less than 10 mm were found to be consistent for all FCH and x values. The novelty of this study is to formulate the optimisation problem in HTS Maglev using the developed ML model by addressing two specific objectives one of which focuses on maximizing Fz while ensuring Fx remains within a defined tolerance (β3), representing the minimum allowable ratio of the levitation force to the total force, and the second problem aims to maximize Fz while obtaining zero Fx. The optimum PMW, FCH, x, and z values were obtained at 30 mm, 30 mm, 4 mm and 5 mm, corresponding to Fz and Fx values of 224.2 N and -53.8 N for option 1. As for option 2, the process parameters were obtained as 28.6 mm, 25.9 mm, 0 mm, and 5 mm, corresponding to Fz and Fx values of 194.2 N and 0 N. It was obtained both experimentally and by the optimization that Fz reaches close its maximum as the Fx gains attractive character. Hence, it is expected that the outcomes of this study will significantly benefit the design of HTS Maglev systems and find valuable applications across various transportation engineering projects.

Influence of Ag Doping on Thermal Conductivity and Magnetic Levitation of Single Grain YBCO Superconductors for High-Temperature Superconducting Maglev

Ag doping in (RE)Ba2Cu3O7−δ [(RE)BCO] bulk high-temperature superconductors has been recognized as an effective way to improve the mechanical and superconducting properties of REBCO bulk superconductors for practical applications such as high-temperature superconducting (HTS) Maglev. Ag2O nanoparticles doped YBCO samples with different doping amounts (x, x varies from 0∼0.5 wt%) were fabricated by Top-Seeded Melt-Growth method (TSMG). The samples’ steady-state thermal conductivity (λ) and the magnetic levitation force (FL) were measured by a testing platform under a similar condition to the HTS Maglev system. The effects of Ag2O doping on the λ and FL of single domain YBCO bulks have been systematically studied. The λ of the c-axis and the ab-plane were calculated through the steady-state heat flow method. We observed that λ increases distinctly when x ≥0.3 wt%. The doping amount of 0.3 wt% has been evidenced to be the optimal value, of which the λ of the c-axis and ab-plane are approximately 52% and 48% higher than the undoped one respectively. According to the results of the FL measurement, we found FL will increase while the relaxation rate of the FL will decrease by adding trace amounts of Ag2O nanoparticles in comparison to the undoped sample. This observation suggests that Ag-doping is an effective way to enhance thermal conductivity as well as the superconducting properties of YBCO superconductors for practical applications.

Study on the Dynamics Characteristics of HTS Maglev Train Considering the Aerodynamic Loads under Crosswinds

High-temperature Superconducting (HTS) maglev trains are vulnerable to the effects of crosswinds when operating at high speeds in open-air conditions, potentially compromising riding comfort and safety. This study established a vehicle dynamic model based on the nonlinear maglev-track relationship and added aerodynamic loads under crosswinds to the train’s simplified load center to address this issue. Using the maximum vibration acceleration limit and the Sperling index, we evaluated the riding comfort of the HTS maglev train under different conditions. Further, the vibration acceleration power spectral density was analyzed to reveal the impact of increasing the train’s operating speed and crosswind speed. The results indicated that the lateral and vertical Sperling index achieved an “excellent” rating, even at crosswind speeds of up to 20.7 m/s when the train was traveling at speeds of up to 600 km/h. However, it was noted that particular attention should be given to the riding comfort in the head car when the speed reaches 600 km/h. Moreover, the influence of the increase in train speed on the vibration frequency domain distribution of the three car bodies and the train’s riding comfort is greater than that of the increase in the crosswind speed. These findings may provide a valuable reference for the future engineering application of the HTS maglev train.

A 6 degrees of freedom electromagnetic–thermal–dynamic coupling model for high-temperature superconducting levitation system

As the main merits, self-stabilization and no magnetic resistance make the high-temperature superconducting (HTS) magnetic levitation technology a crucial area for high-speed magnetic levitation development. To guarantee a stable operation of superconducting magnetic levitation systems, the dynamic characteristics of superconducting bulk materials occupy a significant place. However, in the previous research, there is still a lack of a simulation method that can describe 6 degree of freedom (DOF) motion of the superconductor. In this paper, an electromagnetic–thermal–dynamic coupling calculation model was established first. Then, the damping characteristics of 5-DOF superconducting levitation were experimentally tested, and the response analysis of the superconductor under 1–20 Hz excitation was carried out to explore the coupled motion relationship between the various degrees of freedom of the superconductor. In addition to the above, the operating conditions and primary resonance intervals that should be avoided by the HTS maglev system were identified. Additionally, a numerical simulation was conducted to investigate the dynamic response of the HTS maglev system under impact loads. All in all, this study explored the temperature rise conditions of superconducting bulk materials under excitation force through magnetic-thermal-force multi-physics coupling research. This 6-DOF model can provide a comprehensive simulation method for superconducting maglev systems in superconductor's motion behavior, attitude, and thermal state monitoring.

Diamagnetic Screening in the Electromagnetic Turnout Switch for a High-Temperature Superconducting Maglev System

Maglev systems represent a cutting-edge high-speed transport technology, and turnout switches play a critical role in the creation of a highly branched network. There are two common types of turnouts for high-temperature superconducting (HTS) Maglev systems: mechanical and electromagnetic. Due to the many advantages, an electromagnetic turnout is a better choice for a Maglev system than a mechanical one. However, there is a difference in the distribution of the magnetic field over the turnout area and the permanent magnetic track, which cannot meet the safety requirements of the Maglev system. This article proposes a modernized design of an electromagnetic switch based on previously proposed optimization solutions by placing a diamagnetic screen between two electromagnetic poles of an electromagnet, thereby reducing the scattering fluxes between them. The method of diamagnetic screening and experimental methodology are described in this article. The experiment was carried out using a three-dimensional magnetic field scanner to provide results on the distribution of the magnetic field and the increase in the magnetic induction value over the electromagnet poles. Thus, this article provides valuable suggestions for improving the design of the electromagnetic turnout of HTS Maglev systems. Moreover, the proposed method can be applied to any magnetic device or electric machine with an open magnetic circuit.

Levitation Force Compensation Study for HTS Maglev System Based on the Input of Electromagnetic Force

The advantages of levitation and guidance integration make the high-temperature superconducting (HTS) maglev system have great potential in the field of high-speed transportation. However, due to the influence of some factors such as the Dewar (a low temperature thermostat for superconductors) vacuum increases and magnetic field irregularity, the levitation force will decline and working height will drop. To solve the problems, this paper proposes a compensation method based on electromagnetic auxiliary device. Firstly, the thought and purpose of this method are explained in detail. Secondly, the effectiveness of levitation force compensation is verified by experiment. Then, electromagnetic simulation model is established and its correctness is verified by comparing simulation results and experimental data. Finally, dynamic simulation is conducted based on the verified model to study the vibration characteristics of Dewar system. The results show that the auxiliary device can compensate the levitation force and suppress vibration well. Meanwhile, comparing with the field cooling height (FCH) at 20 mm and 30 mm, the compensation effect of former is better than latter, but the overall maximum levitation force of latter is higher than former. This research provides an economical and effective way to achieve the levitation force compensation of HTS maglev system. Furthermore, the electromagnetic auxiliary device is an active energy input port, providing the possibility for the active control of HTS system. It is expected to provide reference for future practice in relevant application fields.

Working temperature threshold analysis for HTS maglev system based the novel thermal-dynamic levitation force coupling measurement device

The previous researches show that the temperature rises inside the high temperature superconducting (HTS) bulk will affect the levitation performance of the HTS bulk. In order to further explore the relationship between the internal temperature rise and the levitation force of the HTS bulk, a thermal-dynamic levitation force coupling measurement device is reformed, and the Halbach PM wheel is used to generate alternating MF at field cooling height (FCH) 30/40 mm, working height (WH) 8/12 mm and speed from 500 rpm to 3500 rpm with intervals of 500 rpm, to study the influence of MF fluctuation on the temperature rise and levitation force of the HTS bulk. The temperature values are obtained when the levitation force decays greatly (82 K) and fails (87 K). The experimental results can provide theoretical suggestions for the irregularity standard of PMG and reference for the protection of the HTS pinning maglev system.

Novel method to detect the speed and position of the HTS Maglev train by using the TMR sensor and the magnet arrays

Magnetic levitation (Maglev) train’s position and speed detection system facilitates the control of the Maglev train. Yet nearly all previous schemes are unsuitable for the high temperature superconducting (HTS) Maglev train. New sensors and signal sources are expected to improve the system. Here the tunnel magneto resistance (TMR) sensor and the magnetic arrays are used to realize the speed and position detection and the improved automatic multiscale-based peak detection (AMPD) algorithm is applied. Furthermore, the algorithm’s adaptability to various operating conditions is verified and the system can be applied in different working conditions. Finally, a preliminary experimental test is carried out. Such a system, accompanied by the equipment and the algorithm, offers results of accuracies of 95%–97% for speed measurement and 1 cm–3 cm for positioning, providing an avenue to improve the performance of HTS Maglev train’s operating control system.

Aerodynamic load analyses of less-emission HTS maglev train in evacuated tube transport system

An evacuated tube transport (ETT) system is proposed by combining evacuated tube technology and high temperature superconducting (HTS) maglev technology in this paper. It can be predicted that this future transport mode can own the advantages of less emission, low noise, high efficiency, and suitable for high-speed or super-high-speed application. The train running at a high speed will inevitably cause complex aerodynamic load behaviors in an enclosed low-pressure tube. It further affects the real energy consumption and the fatigue life of the components. In order to explore how the aerodynamic load behaves in an ETT-HTS Maglev system, we established a three-dimension numerical calculation model based on ANSYS FLUENT software. The steady aerodynamic loads on the train’s surface and the tube’s inner surface are investigated under different pressures and different operation speeds. It is found that the aerodynamic load on the surface of the train and tube is significantly affected by the pressure inside the tube and the running speed of the train. The aerodynamic load fluctuations at the rear of the train are relatively more violent than those at the head. We also found that the impact of compression wave and expansion wave on aerodynamic loads at different positions of the tube is related to the size of the flow field space between the tube and the train. These results can provide some reference for the less-emission train body design and the whole ETT-HTS Maglev system structural strength in the near future.

Simulation Analysis and Online Monitoring of Suspension Frame of Maglev Train

A maglev train is a new type of high-speed railway transportation. A high-temperature superconducting (HTS) maglev system is one of the typical representatives in the field of maglev trains. In order to research the levitation characteristics of an HTS maglev train, the force characteristics and operation performance of the train were researched. However, at present, there is still no research that simulates the real load situation of a running maglev train while analyzing the suspension frame. Regarding this issue, in this paper, the suspension frame is simulated and analyzed to simulate the real load situation of a maglev train. The results show that the suspension frame of an HTS maglev train can bear corresponding loads under different working conditions, and its strength and stiffness meet the requirements of use, safety, and reliability. Random irregularity in the permanent magnet track of an HTS maglev train route is inevitable, which will make the suspension frame produce a vibration response under different running speeds of the train. Vibration of the suspension frame of the train is inevitable. For the electromagnetic levitation (EMS) train, researchers considered monitoring the train status. However, at present, there is no suspension frame condition monitoring device for an HTS maglev train. In addition, the levitation height of the suspension frame affects the suspension performance and traction performance of the vehicle, and the vibration of the suspension frame during running affects the dynamic performance and safety of the suspension frame and the vehicle. Regarding the issue above, through a suspension frame monitoring system, the lateral and vertical vibration acceleration and levitation height of the suspension frame are monitored at different train speeds. The maximum value of vibration acceleration and the fluctuation range of levitation height are within the safe range. It is verified that the simulation analysis of the suspension frame of an HTS maglev train is correct, the suspension frame is safe, and the train can run safely.

Vertical Dynamic Response Analysis of HTS Maglev Vehicle Excited by a Designed Coreless-Typed PMLSM

High-temperature superconducting (HTS) pinning maglev has the potential for high-speed application because of its advantages of passive self-stabilization, energy conservation, environmental protection, and no inherent magnetic resistance along the forward direction. The HTS pinning maglev can realize non-contact levitation and guidance. Permanent magnet linear synchronous motor (PMLSM) is suitable for HTS pinning maglev to realize non-contact drive. However, in addition to the longitudinal driving force for the HTS pinning maglev train, the PMLSM also produces the normal force which will cause additional excitation on the maglev train and affect its levitation height and vertical dynamic response. In this paper, a coreless-typed PMLSM is designed for HTS pinning maglev driving system, and the driving force and normal force characteristics of the motor under different air gaps are calculated. Then, a vertical dynamic model of the HTS pinning maglev vehicle is established. The vertical dynamic response of the HTS pinning maglev vehicle excited by the normal force of PMLSM and permanent magnet guideway (PMG) irregularity is simulated and analyzed. This work can provide a reference for the study of the electromechanical coupling effect between the HTS pinning maglev levitation system and linear motor driving system.

Lateral Dynamic Performance of High-Temperature Superconducting Pinning Maglev Vehicle Driven by Electrodynamic Wheel at Medium and Low Speed

High-temperature superconducting (HTS) pinning maglev has the advantages of self-stationarity, low noise and resistance. This technology can be applied in urban rail transit, such as straddle-type monorail vehicles. Due to the limited space for placing the drive device above the track, electrodynamic wheel (EDW) drive can be applied effectively utilizing the ample space on both sides of the track, realizing contactless drive. In this paper, the lateral dynamic performance of an HTS pinning maglev vehicle driven by EDW is analyzed. Initially, 2-D transient simulations under various rotational speeds of the EDW are conducted. The influence of different working air gaps on the device's normal force and propulsion force is analyzed. Subsequently, a dynamic model of HTS pinning maglev vehicle with EDW is established. EDW's influence on the lateral dynamic performance of HTS pinning maglev vehicle is analyzed, and the lateral dynamic performance of the vehicle at various speeds is simulated. The results show that the HTS pinning maglev vehicle driven by EDW has good lateral dynamic performance in the low and medium speed range, and EDW can effectively improve the lateral stationarity of HTS pinning maglev vehicle. This study can provide a new driving mode for HTS pinning maglev vehicle and reference for improving and optimizing the existing medium and low speed straddle-type monorail vehicles with HTS maglev technology.