High-speed Vehicle Research Articles

Numerical Simulation of the Horizontal Water-Entry Process of High-Speed Vehicles

Based on the RNG k-ε turbulence model and VOF multiphase flow model, a numerical model of horizontal water-entry of the vehicle was established, and the numerical method was verified by experimental results. The cavitation characteristics, fluid resistance, and motion of the vehicle under different conditions were studied during the vehicle’s water-entry process. The results show that the cavitation process can be divided into the cavity development stage, saturation stage, and collapse stage. With the increase in initial velocity and mass of the vehicle, more water vapor will be generated during the water-entry process. The initial velocity of the vehicle had a limited effect on the resistance coefficient. The resistance coefficient in the stable stage remained almost unchanged for vehicles with different masses. Nevertheless, the time interval of the stable stage was shortened, and the resistance coefficient was greater in the gradually increasing stage for the vehicle with a smaller mass. For vehicles with higher initial velocity or smaller mass, the instantaneous velocity decreased faster after it entered the water. The vehicle with a streamlined design was able to reduce the generation of water vapor and decrease fluid resistance and its coefficient, and the vehicle can run farther during the water-entry process.

Effects of Wheel Flats on Vibration and Stress Response of the Wheel-Rail System in High-Speed Trains

With the advancement of high-speed and lightweight vehicles, the occurrence of wheel tread wear, including wheel flats, has escalated. The resulting impact loads on axle-end components and the dynamic response of the axle cannot be overlooked. On-track tests were conducted on wheel flats to obtain wheel-rail forces, axle box vibration accelerations, and axle stresses during service. Time–frequency analysis was employed to uncover patterns of variation with speed. Additionally, a dynamic model of the high-speed train–track system was developed to replicate test conditions, investigating the characteristics of wheel–rail loads and structural elastic vibrations under high-frequency excitation for various flat sizes and higher operating speeds. The findings reveal that under wheel flats, the time-domain response of the wheel–rail system exhibits periodic impacts, while the frequency-domain shows high-frequency energy comprising multiple harmonics of the wheel rotation frequency. Wheel–rail forces, axle box vibration accelerations, and axle stresses exhibit inflection points with increasing speed, particularly within the 120–160 km/h range. In the high-frequency domain, axle stresses display characteristic frequencies that remain unchanged with speed, attributed to the coupled vertical bending vibration modes of the wheel–rail system. These research results offer foundational support for predicting fatigue damage to axle-end components, assessing axle stress, and establishing tolerances for tread defect limits.

Lightweight, thermally insulating SiBCN/Al2O3 ceramic aerogel with enhanced high-temperature resistance and electromagnetic wave absorption performance

Owing to tunable dielectric properties, light weight and high porosity, polymer-derived SiBCN ceramic aerogels possess significant application prospects in electromagnetic wave (EMW) absorption and thermal insulation. However, due to inadequate oxidation resistance, the structural collapse and performance deterioration of SiBCN aerogels will easily occur in high-temperature aerobic environments, limiting their application. Herein, to address this issue, a novel and straightforward strategy based on typical polymer-derived-ceramic (PDC) aerogel method and impregnation with boehmite sol was proposed for synthesizing SiBCN/Al2O3 composite ceramic aerogels. The microstructure, phase composition, thermal insulation, oxidation resistance and EMW absorption properties of SiBCN/Al2O3 ceramic aerogels were investigated. The resulting SiBCN/Al2O3 composite aerogel demonstrates superior high-temperature structural stability, exhibiting an ultra-low linear shrinkage of only 6.5 % following heat treatment at 1200 °C for 2 h in air. Additionally, the composite aerogel shows a low thermal conductivity of 0.039 W/mK and a low density of 0.112 g/cm3. The SiBCN/Al2O3 composite aerogel, composed of dielectric SiBCN, conductive free carbon, and insulating alumina, demonstrates outstanding EMW absorption properties with a minimum reflection loss of −48.6 dB and an effective bandwidth of 5.8 GHz. The enhanced microwave absorption performance is mainly attributed to the improved impedance matching, multiple reflection, and enhanced interfacial polarization resulting from the introduction of Al2O3. Given prominent oxidation resistance, thermal insulation and EMW absorption properties, the SiBCN/Al2O3 composite aerogel paves the way for developing microwave absorption and thermal insulation integrated material in high-speed vehicles.

Validation of heat transfer models and optimization of heat shielding performance of high-temperature multilayer insulations for hypersonic vehicles

Multilayer insulation (MLI) is widely used in hypersonic vehicles because of its low density and excellent thermal insulation performance. However, the insulation mechanism of MLI remains poorly understood, leading to conflicting views on how to enhance its thermal insulation capabilities. In this study, two different numerical models were built and validated with experiment data to investigate key factors influencing MLI performance. The analysis focused on the effects of reflective screen positioning, the surface emissivity of reflective screens and the radiation properties parameters of fibrous materials on the thermal insulation performance of the MLI. The results show that the thermal insulation performance is better when the reflective screens are placed close to the thermal boundary. Moreover, insulation materials with lower absorption coefficients enhance the effectiveness of the reflective screens, further improving the thermal insulation performance of MLI. In addition, the study reveals that the thermal insulation mechanisms differ between the upper and lower surfaces of the reflective screens. Lower emissivity on the upper surface combined with higher emissivity on the lower surface optimizes the thermal insulation performance of MLI. These findings offer valuable insights for advancing MLI designs and improving its application in future high-speed vehicles.

Numerical Solution of Burgers Equation Using Finite Difference Methods: Analysis of Shock Waves in Aircraft Dynamics

In this research, the Lax, the Upwind, and the MacCormack finite difference methods are applied to the experimental solving of the one-dimensional (1D) unsteady Burger's Equation, a Hyperbolic Partial Differential Equation. These three numerical analysis-solving methods are implemented for accurate modeling of shock wave behavior high-speed flows that are necessary for aerospace engineering design. This research analysis proves that the MacCormack technique is the one that treats the differential equations with second-order accuracy. This method is quite preferred when it comes to numerical simulations because of its advanced level of accuracy. Although the Upwind and Lax methods are slightly less accurate, they show the development of shock waves that give visualizations to better understand the flow dynamics. Also, in this study, the impact of varying viscosity coefficients on fluid flow characteristics by using the lax (a numerical method for solving the viscous Burgers equation) is investigated. This identification of the phenomenon sheds light on the behavior of boundary layers, which, in turn, can be used to improve the design of high-speed vehicles and lead to a greater understanding of the area of ​​fluid dynamics.

A hybrid triboelectric-piezoelectric-electromagnetic generator with the high output performance for vibration energy harvesting of high-speed railway vehicles

With the rapid development of intelligent high-speed train, people's travel becomes more convenient, time-saving and comfortable. However, the increase in the number of equipped electronic facilities also brings more power consumption. While the ultra-high voltage drive power system cannot directly drive its numerous devices and the vibrational energy of high-speed trains is completely abandoned. Herein, a hybrid triboelectric-piezoelectric-electromagnetic generator (HTG) is proposed to drive the signal and sensing devices of high-speed train by in-situ harvesting the corresponding vibration energy. Compared with commercial polyformaldehyde film, the output power of triboelectric nanogenerator with the polyformaldehyde nanofiber film prepared by electrospinning technology is improved by 130 times. Furthermore, thanks to the high space utilization and output performance, the HTG has achieved a power-density of the order of kW/m3, which is an improvement of 1–3 orders of magnitude compared to previous research work on vibration energy collection. Importantly, the self-powered wireless motion monitoring system based on HTG can realize real-time monitoring and transmission of motion information such as speed, frequency and displacement. This finding not only gives an important way to efficiently harvest vibration energy, but also provides new ideas for the design of more economical, comfortable and intelligent high-speed trains.

Comparative analysis of ride comfort evaluation indices of high-speed vehicles based on a vehicle-seat-human body coupled dynamics model

As high-speed vehicles become increasingly lightweight, the influence of passengers on the vehicle vibration system cannot be overlooked. In this paper, a 3D vehicle-seat-human body coupled dynamics model is established to comprehensively evaluate the ride comfort of high-speed vehicles. The model combines the passenger biomechanics with the carbody flexibility. This is often neglected in previous studies and only the carbody vibrations are considered. Applying the validated model, four types of ride comfort evaluation indices are calculated and compared at 250–400 km/h. Results show that the ride comfort of high-speed vehicles at different speeds is excellent when the carbody acceleration and Sperling indices are used. While the results are significantly different when the total equivalent weighted acceleration and annoyance rate indices based on human body vibrations are used. At full load and speed of 400 km/h, the passengers sitting near the windows at both ends of the carbody felt ‘slightly uncomfortable’ or ‘less comfortable’ with an annoyance rate of about 30%, which indicates that up to 30% of the passengers might find the vibrations intolerable. This study underscores the necessity of integrating human body vibrations and passenger subjective psychology into ride comfort assessments, which can provide theory references for the selection and optimization of evaluation indices for high-speed lightweight vehicles.

Fatigue properties of non-press-fitted part of full-scale induction-hardened axles of medium-carbon steel for high-speed railway vehicles

This study aimed to examine the stress–number of cycles (S–N) curve and fatigue limit of non-press-fitted parts to improve the sophistication of the design method of induction-hardened axles for medium-carbon steel high-speed railway cars. Macroscopic cracks were generated in the non-press-fitted parts of the axles by selecting appropriate fatigue test methods. Thus, the S–N curve was approximated, and the fatigue limit was obtained. The value of an index in the power-law expression of the S–N curve was 11, which was proposed to fatigue damage evaluation standard. Moreover, we constructed a prediction model for high-and very-high-cycle fatigue limits based on the local fatigue-limit approach and fatigue test results of cut-out specimens from several depth regions of induction-hardened axles. The fatigue limit predicted by the model agrees with the experimental high-cycle fatigue limit. The model estimated that the fatigue limit did not decrease in the very-high-cycle regime.

An Investigation of Internal Drag Correction Methodology for Wind Tunnel Test Data in a High-Speed Air-Breathing Vehicle Using Numerical Analysis

AbstractAccurate understanding of aerodynamic characteristics is critical for air vehicle design. This study applies the impulse-momentum theorem to estimate internal drag of an asymmetric air vehicle. Both computational fluid dynamics (CFD) and wind tunnel tests were employed. Numerical analysis using STAR-CCM + was conducted across various Mach numbers, while wind tunnel tests were conducted under only specific Mach number conditions. The measured data from wind tunnel tests, which is considered representative, were compared with CFD plane-averaged values, indicating fairly good agreement. However, discrepancies arose when comparing CFD cell-averaged values with the plane-averaged values. To address this, a correction function was developed to describe the differences. It was observed that the ratio of internal drag coefficient from the cell-averaged values to that of the plane-averaged values followed an exponential function of Mach number. This approach allows wind tunnel data to be transformed into a form akin to cell-averaged values, enhancing internal drag estimation accuracy. Future research will explore additional methodologies to further refine and validate the proposed approach.

Management of Comminuted Frontal Depressed Fracture Using Split Calvarial Graft: A Novel Technique

AbstractFrontal depressed fracture generally results from high-speed motor vehicle accidents. The frontal fractures can be closed or open depending upon the involvement of the overlying skin. Frontal fracture can be comminuted if the bone is broken in at least two or more places. Because of the proximity of the frontal bone to critical structures like the frontal sinus, frontal dura with underlying brain parenchyma, and orbit with its content, an injury resulting in a frontal depressed fracture can result in a multitude of clinical symptoms. If not addressed promptly with an experienced team, these fractures can result in cerebrospinal fluid leak, osteomyelitis of the frontal bone, meningitis, and ocular and olfactory dysfunction with poor cosmetic outcomes. Thus, repairing the frontal depressed fracture should be considered a priority. The standard practice is to elevate the depressed fracture and repair any dural defect. In case of a comminuted fracture, elevation is not possible, and we generally remove the fracture pieces and repair the defect using titanium mesh. In this case report, we propose a novel technique of repair of the defect using a split calvarial graft, which is fashioned after separating the outer table from the inner table of the posterior frontal bone. This technique reduces the theoretical risk of infection and is cost-effective as our procedure does not require any external implant in cranioplasty.

Analytical study and control of high-speed vehicle hunting stability with traction/braking torque

Analytical study and control of high-speed vehicle hunting stability with traction/braking torque

A-123 Comparative Assessment of Unmanned High-Speed Aerial Vehicles in Medical Logistics: Blood Sample Transportation Amidst Weather Variability

Abstract Background Drones, as an innovative technology, hold transformative potential in the field of medical logistics, especially in the transportation of sensitive medical materials like blood samples. This study aimed to assess and compare the impact of high-speed drone transportation with conventional car transportation on the integrity and preanalytics of blood samples, taking into account various blood materials and analytes. Methods Blood samples, including EDTA whole blood, serum, and plasma anticoagulated with Citrate and Lithium-Heparin transported as whole blood, were subjected to transportation via both drone and car. Drone flights were tested under diverse weather conditions (ranging between 4 and 20 degrees Celsius), and results were compared to samples stored without transportation. The maximum drone speed exceeded 100 km/h. A total of 28 analytes were tested on Serum, 20 on EDTA, 26 on Lithium-Heparin, and 5 on Citrate blood. Statistical analyses were performed using Passing Bablok and Bland-Altman methods. Results For Serum samples, the correlation coefficient (r) ranged from 0.830 to 1.000, and slopes varied from 0.913 to 1.111. Five analytes (total bilirubin, Calcium, Ferritin, Kalium, and Sodium) exhibited discrepancies between the negative control and the transported sample, with r lower than 0.800, slopes not between 0.8 and 1.2, and mean (%) not between +/- 10%. However, no significant differences were noted between drone and car transportation. Similar patterns emerged for EDTA, Lithium-Heparin, and Citrate samples, with r ranging from 0.829 to 0.997, 0.939 to 0.998, and 0.830 to 1.000, respectively. Slopes ranged from 0.956 to 1.051, 0.938 to 1.085, and 0.913 to 1.111. Despite identifying a few discrepancies in specific analytes, no significant differences were observed between transportation methods. Conclusions n comparison to transportation by car, drone transportation of blood samples did not lead to alterations in concentrations of commonly used analytes. Notably, instances of differences before and after transportation were attributed to the transportation process itself rather than the mode of transportation. This suggests that the use of drones for medical sample transport can be deemed comparable to, if not superior to, traditional car transportation methods.

Development of means for suppressing the negative effects of interaction between the pilot and reentry and other high-speed vehicles

Several novel active and passive means for the suppression of pilot-induced oscillations are considered in the paper. The potential of the proposed means in eliminating Category I, II, and III pilot-induced oscillations was studied in ground-based simulation for two controlled element dynamics corresponding to an aerospace vehicle and a second-generation supersonic transport. The experiments demonstrated that the highest effectiveness in suppressing pilot-induced oscillations and improving task performance is provided by integrating both proposed active suppressors with one of the passive prefilters.

Study on Aerodynamic Characteristics and Stability of a Vehicle with Inverted Dihedral and Momentum Lift Augmentation

Abstract Inspired by the wave-rider idea and momentum principle, the vehicle with inverted dihedral and momentum lift augmentation is a new aerodynamic configuration of high-speed gliding vehicle in the near-space, which has achieved a high lift-to-drag ratio and long-distance sliding. Numerical simulation of aerodynamic characteristics and stability of the aircraft are carried out in this paper. The lift-to-drag characteristics, longitudinal-directional stability and lateral-directional stability are evaluated based on the National Numerical Wind tunnel’s high-speed simulation software, named NNW-HyFLOW. An unstructured/hybrid grid is used in the calculation at the typical ballistic points of altitude of 10-75km and Mach number of 3-25. The results shows that the lift-to-drag ratio reaches a peak value of 4.11 at the altitude of 30km and attack angle of 8°. This value is decreased when the altitude raises. The usable lift-to-drag ratio is over 3 in the glide phase range from 30 to 50 kilometres. This vehicle shows better longitudinal-directional stability at large angles of attack than at small in the reentry phase and glide phase, which can be optimized by adjusting the center of mass or pitching rudder. It has a weak instability in the lateral direction at small angle of attack in the glide phase. Therefore, it is suggested to avoid to work at the high altitude with a small angle of attack. Or, the lateral-directional stability can be strengthened at this altitude by improving the V-tail.

A novel wheel wear indicator in regard to wheel-rail contact parameters and vehicle hunting stability

It is well known that the abnormal equivalent conicity caused by wheel and rail wear is the main root of hunting instability, but it is still difficult to trace the underlying factor when the dynamic instability occurs, that is, wheel wear induced, rail wear induced or both. To face this challenge problem, this paper constructed a novel wheel wear indicator based on the moved wear area difference. The long-term tracking test data of different wheel profiles were used to analyze the correlation between the wear indicators and the wheel-rail contact parameters. A fully detailed dynamic model of one typical high-speed railway vehicle was developed to investigate the evolution of vehicle hunting stability under the variation of the proposed wear indicator. The results indicate that the proposed wear indicator based on the moved wear area difference has a strong correlation with the equivalent conicity and can be used for the estimation of wheel-rail contact conditions. Furthermore, the hunting stability and the instability form is closely related to the value of the proposed wheel wear indicator, which is helpful to trace the underlying factor of hunting instability, thereby supporting intelligent operation and maintenance of railway vehicles.

Thermally insulated C/SiC/SiBCN composite ceramic aerogel with enhanced electromagnetic wave absorption performance

Thermal insulation and electromagnetic wave (EMW) absorption integrated materials with lightweight are highly desirable in hypersonic vehicles and military application, as they provide both aerodynamic heat resistance and EMW stealth capability. Herein, a C/SiC/SiBCN ceramic composite aerogel was developed using a novel strategy combining in situ chemical vapor deposition of SiC nanofibers with the polymer-derived ceramic (PDC) aerogel method. The microstructure, phase composition, thermal insulation, mechanical properties and EMW absorption performances of the composite aerogel were thoroughly investigated. The resulting C/SiC/SiBCN composite aerogel with three impregnation-pyrolysis cycles demonstrates improved mechanical properties, with the compressive strength increasing from 0.21 MPa to 0.48 MPa compared to pure SiBCN aerogel. Additionally, the composite aerogel shows a low thermal conductivity of 0.049 W/mK and a low density of 0.116 g/cm3. Moreover, the C/SiC/SiBCN composite aerogel exhibits outstanding EMW absorption properties, achieving a minimum reflection loss of -45.7 dB and an effective bandwidth of 5.3 GHz. Owing to the integration of EMW absorption and thermal insulation properties, the C/SiC/SiBCN composite aerogel offers promising potential for developing integrated microwave absorption and thermal insulation materials for high-speed vehicles.

Study of the C-γ-Reθ Transition Model Based on the NNW-HyFLOW Software

Abstract Since the release of hypersonic computational fluid software NNW-HyFLOW in 2023, its computational modules have been continuously expanded for the development needs of hypersonic vehicles. The C-γ-Reθ transition model has been developed based in the framework of the NNW-HyFLOW to expand the prediction of transition in the design of high-speed vehicles. Firstly, the calibration of two basic relations of Re θc and Flength which is originally designed for the low-speed flat plate cases have been realized and expanded to high-speed flows. Secondly, the the empirical formula of Mach number correction has been adjusted by several typical high-speed transition cases. The same correction also has been made to the turbulence Prandtl number correction following the sae procedure. A crossflow transition module has been added with the calibration of the crossflow Reynolds number and validation of the experiment data of the HyTRV lifting body. The numerical tests show that the C-γ-Reθ transition model based on NNW-HyFLOW software has been basically realized with the ability of steamwise transition and crossflow transition prediction.

Multiscale modeling of cavitation around high-speed object based on Euler-Lagrange model and overset mesh

Abstract Cavitation is a common phenomenon, which usually occurs inside the high-speed liquid or at the liquid-solid interface. The unsteady behaviors of cavitating flow, such as shedding and collapse, can cause intense pressure fluctuations and reduce the stability of devices such as under-water high-speed vehicles. In addition, cavitating flow changes the dynamic characteristics of the liquid and causes vibration of the structure as well, making it extremely difficult in achieving precise control. Using OpenFOAM, the present work employs the large eddy simulation (LES) approach to investigate the characteristics of the unsteady cavitating flow around a high-speed under-water object with using the overset mesh technology. The volume of fluid (VOF) approach jointed with the Lagrangian discreate bubble model (DBM) is used for capturing the multiscale cavitation features. The Schnerr & Sauer model is applied for the mass transfer between water and vapor in macroscale, while the Reynolds-Pel equation is incorporated for the growing and collapsing of microscale bubbles. Due to the difficulty in incorporating the multi-scale method into the problems with mesh motion, the present work employs the overset mesh method. Compared with the published small-scale water tank experiment, the LES simulation results fit well with the experimental phenomena, and the DBM can capture the small bubbles accurately. On the basis of model verification, the mechanisms of cavitation forming and collapsing is investigated and the effect of cavitation shedding on the motion of the object is also studied. Moreover, the nucleation, growth, collapse of bubbles, and the interaction between discrete bubbles and large cavities can be well revealed. Further, the multi-scale Euler-Lagrange model is also applied in the rotating propeller, the generation of tip vortex cavitation which is hard to be captured by traditional models is well presented.

Discrete element method simulation of high-speed vehicle collisions with road barrier systems

AbstractThe behavior of road or perimeter protection barriers under vehicle impact are usually investigated based on crash tests and finite element (FE) numerical approaches, which are ether expensive or time-consuming. Several studies have proposed to reduce the computation time of the numerical analysis by substituting the complex FE models of vehicles using simplified mass–spring–damper system models. However, these models have drawbacks since consideration of different vehicle impact angles is difficult and they are unable to correctly simulate the risk of high-speed vehicle collision running over the barrier. In this paper, a new approach is proposed to simulate the collision of vehicles with barriers based on the discrete element method (DEM). Here, to save computation time only a handful of 3D non-spherical particles are used to represent the barrier and vehicle. These particles are generated based on the super-quadric function, which is capable of generating a variety of shapes needed for the model. The contact detection and evaluation are carried out based on discrete function representation of the particles with uniform sampling. The bond between two discrete elements is defined using a nonlinear cohesive beam model since the distance between the elements is relatively large. The simulation results obtained based on this approach are more accurate and complete than the simplified mass–spring models and computationally more efficient than the FE model.

An examination of high-speed aircraft – Part 2: Safety and reliability

This paper presents a detailed accident investigation into incidents involving high-speed vehicles, particularly supersonic and hypersonic platforms. Examining challenges related to engine performance, structural integrity, and economic aspects in military aerospace, the study emphasizes the importance of real-time health monitoring systems. A key highlight is the exploration of how these systems support the autonomy of hypersonic vehicle. While recognizing challenges related to sensitive technologies and data, the paper outlines research directions encompassing human factors, simulation and training programs, and policy advocacy for integrating high-speed aircraft into existing airspaces. In summary, this research contributes valuable insights to the understanding of high-speed aviation accidents, with implications for improving safety and efficiency in the future and ultimately shows that high-speed aviation safety cannot be treated in the same manner as its subsonic counterpart.