Journal of Mechanical Science and Technology最新文献

Large quantities of sand carried by crosswinds often settle in the cabin of diesel locomotives operating in desert regions. This study adopts an Euler-Lagrange two-phase flow model to simulate sand movement and deposition in a running diesel locomotive through the ventilation grilles. The realistic sand particle diameter distribution obtained from the field test is incorporated by the Rosin-Rummler model in computational fluid dynamics software. The realizable k-ε turbulent model is adopted to simulate the turbulence. The operation of the locomotive on a straight track at 200 km/h with five different crosswind velocities is studied numerically. The simulation results indicate that the increment of crosswind speed leads to higher pressure on the grille and the velocity of the internal flow field. The relationship between the number of sand particles trapped inside the car and the incident angle (i.e., resultant wind angle) is discovered. It is evident that the majority of sand particles enter the compartment through the windward tail grilles. Therefore, the influence of adjusting the tilt angle of the tail grille on the sand entering the locomotive cabin is calculated. It is discovered that the compartment experiences the least sand deposition at a 30° title angle. Therefore, optimizing the tilt angle of the frame for grilles can significantly enhance the filtering of the grille.

The reduction of wheel-rail wear is a fundamental task in railway engineering that significantly affects the operating performance in the lifecycle. To improve the dynamic response and profile wear evolution performance of wheel-rail interaction, a shape optimization procedure for the railway wheel profile is proposed. First, the geometry modeling method, which ensures the continuity of first-order derivation of the wheel profile, is introduced to generate a large number of candidate profiles, and multibody dynamics simulation is conducted to analyze the dynamics response of the wheel profiles, including wear index, lateral force, lateral acceleration of the frame and derailment coefficient. Then, the Kriging model is constructed to establish the relationship between the design variables and objectives obtained by multibody dynamics simulation, and particle swarm optimization (PSO) is employed to evaluate the optimal parameters for wheel profile that simultaneously considers wheel wear, stability, and lateral force. Finally, the performance of the wheel-rail interaction is evaluated to demonstrate the effectiveness of the proposed method. The numerical simulation result indicates that the optimized wheel profile not only has good performance, including contact state, pressure, and friction at the design stage, but also the physical performance is acceptable after a long-term profile evolution during service, which the maximum wear depth of the optimal wheel profile averagely decreases over 10 % in long-term wear evolution.

The full loss data for the IS (inlet squealer) tip with the wide changes of squealer height (h_st) and tip clearance (h) are measured in an aeroengine turbine blade cascade of downstream-to-upstream velocity ratio (VR) = 2.01 with a five-hole probe instrumentation system. The loss map shows that the variation of IS tip loss with hst/s is strongly dependent upon h/s, contrary to the full squealer tip case. The IS tip loss tends to increase with h_st/s for low h/s, whereas it tends to decrease with h_st/s for high h/s. The noticeable loss reduction by the IS tip can be attained when h/s ≥ 1.5 % especially for high hst/s. The comparison among IS tip losses in three cascades of VR = 1.2 (weak reaction), 2.01 (medium reaction), and 2.4 (strong reaction) reveals that the IS tip-to-flat tip loss ratio is affected considerably by VR (turbine reaction).

An effective oil separating technique from water-oil mixture can be used in various industrial fields such as environmental purification and resource recycling. In this study, a vitreous carbon (VC) grid structure was fabricated by carbonization of digital light processing (DLP) 3D (3-dimensional) printed parts, and its oil separation performance was evaluated. A planner DVC grid structure with pore sizes of ∼200, ∼430 and ∼520 µm was fabricated and its water-oil separation performance werewas evaluated. Despite theoretical calculations suggesting adequate water repelling pressures for pores around ∼300 and ∼360 µm, actual performance fell short due to defects from 3D printing and carbonization processes. A more robust design approach involves fabricating a cuboid shell-shaped VC grid structure with smaller pores (∼150 µm), demonstrating continuous water-oil separation capabilities.

This study developed a dynamic simulation model of hydrogen refueling station (HRS) for the refueling process from high-pressure bank (HPB) to vehicle tank (VT) of fuel cell electric vehicle (FCEV). The model validation was confirmed by comparison with the results from the experimental test of Society of Automotive Engineers (SAE) J2601 protocol. After the validation, the same components and their specifications are used for the analysis of the refueling characteristics in various initial and boundary conditions by a commercial process simulator (Aspen HYSYS). The pressure and temperature profiles of the VT and external temperature conditions were defined for the analysis of the hydrogen refueling characteristics. The dynamic simulation model was in a good agreement with the experimental data and supports to evaluate hydrogen refueling efficiency by the analysis of refueling characteristics.

A method utilizing an embedded sensing system to determine the dynamic load is proposed to address the problem of not being able to directly obtain the dynamic load time history of a crawler driving structure in the harsh underground working environment of a coal mine roadheader robot. A crawler driving structure and its embedded sensing system are designed. A rigid–flexible coupling simulation model of the roadheader robot is established, and the dynamic load time history parameters of the crawler obtained from the simulation and test data are compared and analyzed. Results show that the load fluctuation of the tested track plate at the idler and sprocket is significant. By contrast, the fluctuation of the free segment is minimal. The load fluctuation range of the support segment of the hard road is −5–15 MPa, and that of the soft sand road is −10–25 MPa. Moreover, the track plate exhibits noticeable warping and winding phenomenon relative to the road wheel on the soft sand road. The changing trend of the crawler dynamic load time history obtained from simulation and test is relatively consistent. This study provides a reference for the crawler driving structure’s structural optimization and reliability research.

The paper presents a new active control algorithm for the active cancellation of vibroacoustic noise radiated from the compressor installed under each passenger’s seat in autonomous bus. The compressor is used for a heating, ventilation, and air-conditioning (HVAC) system which provide air conditioning for each passenger in autonomous bus. The sound radiated from the compressor of the HVAC system is a high-frequency annoyance noise caused by vibroacoustic noise due to the shell vibration of the compressor. The dominant frequency components of the vibroacoustic noise are harmonics of the rotation frequency of the reciprocating compressor. The HVAC system generates vibroacoustic noise dominantly in the frequency range between 200 and 600 Hz. Such noise is not only distinctly perceptible but also contributes to passenger discomfort and negatively impacts the perceived quality of the vehicle. The aim of this paper is to attenuate the vibroacoustic noise of the HVAC system by developing an active noise control (ANC) system. Generally, the widely recognized filtered-X least mean squared (FXLMS) algorithm has been successfully implemented to active noise control of reciprocating compressor. However, its performance was found lacking outside the peak frequency of compressor operation noise. To address this, the conjugate gradient algorithm was employed to enhance ANC performance. The conjugate gradient algorithm has a lower residual error and faster convergence rate compared to the FXLMS algorithm. As a consequence, the implementation of the conjugate gradient-based ANC algorithm resulted in enhanced noise reduction not only at the peak frequencies, which correspond to the compressor operation frequency, but also in frequency ranges outside these peak frequencies.

The rapid growth of 3D printing technology has transformed different fields in medicine, for example the fabrication of medical phantoms - physical models mimicking biological tissue in medical imaging and therapy. These phantoms play a crucial role in quality assurance, education, research and training. Unlike traditional methods, 3D printing enables the creation of anatomically accurate, cost-effective, modular, and customizable phantoms with high geometric freedom. A key advantage is the ability to produce patient-based models, tailored to individual anatomies and pathologies using medical imaging data. The workflow involves processing imaging data, refining 3D models, and selecting suitable 3D printing materials. This overview focuses on the workflow, types of phantoms, and the selection of printing techniques and materials. Besides numerous opportunities, challenges include standardization, validation procedures, and ensuring reliability across different systems. The potential of 3D printing in medical phantom development is evident, promising realistic, cost-effective, and personalized solutions for improved medical research.

In order to understand the coking process, the effects of thermophysical properties were investigated during coal carbonization, which significantly affects the heat transfer in the coke oven process. Based on Einstein’s quantum theory and temperature-dependent fits, the specific heat of coal was examined to ascertain its behavior during thermal degradation. The endothermic reactions reported were directly responsible for the influence of high specific heat, and the secondary volatile species rising at high temperatures proves the significance of an exothermic reaction. The effect of porosity due to lump coke and fissures establishes the characteristics of the semi-coke porous structure, and an increase in overall porosity raises the true density of the coke material. The thermal conductivity explains the correlation between particulate and semi-coke charges, and thereby the abrupt increase in conductivity was due to the radiative contribution after the resolidification of coal. Finally, some concluding remarks were presented.

A new eddy current sensor with planar coils designed for noncontact distance measurement was applied in the inter electrode gap detection in the electrochemical machining (ECM). The sensor consists of two micro electroforming planar coils (driver coil and sensitive coil) stacked on the magnetic core. The magnetic model of the detection principle was built, and a new micro motion system was developed as a test and machining platform also. The size of the sensor was: Φ5 mm × 1.5 mm. The results show that the sensor is compact enough to nondestructively assess the electrode gap distance and could be easily integrated into a tool cathode for real-time electrolytic machining gap detection.