Search Results (11)

This study investigated the performance of Savonius hydrokinetic turbine blades through three-dimensional computational fluid dynamics simulations conducted at a fixed tip speed ratio of 0.87. A multi-factor experimental design was employed to construct 45 V-shaped rotor blade models, systematically examining the effects of a V-angle (30–140°) and straight-edge length (0.24 L–0.62 L) on hydrodynamic performance, where L = 25.46 mm (the baseline length of the straight edge). The results indicate that, as the V-angle and the straight-edge length vary independently, the performance of each blade first increases and then decreases. At TSR = 0.87, the maximum power coefficient (C_P) of 0.2345 is achieved by the blade with a 70° V-Angle and a straight edge length of 0.335 L. Pressure and velocity field analyses reveal that appropriate geometric adjustments can optimize the high-pressure zone on the advancing blade and suppress negative torque on the returning blade, thereby increasing net output. The influence mechanisms of the V-angle and straight-edge length variations on blade performance were further explored and summarized through a comparative analysis of the vorticity characteristics. This study established a detailed performance dataset, providing theoretical and empirical support for V-shaped rotor blade design studies and offering engineering guidance for the effective use of low-flow hydropower. Full article

Face milling with end-mill tools represents a solution for woodworking applications on small-scale or complex surfaces, but information regarding the surface quality per specific tool type, wood material, and processing parameters is still limited. Therefore, this study examined the surface quality of tangential oak and maple CNC face-milled with two end-mill tools—straight-edged and helical—for three values of stepover (5, 7, 9 mm) and two cutting depths (1 and 3 mm). The surface quality was analyzed with roughness parameters, roughness profiles, and stereomicroscopic images and was referenced to that of very smooth surfaces obtained by super finishing. The helical end mill caused significant fiber tearing in maple and disrupted vessel outlines, while prominent tool marks such as regular ridges across the grain were noticed in oak. The best surface roughness was obtained in the case of the straight-edged tool and minimum stepover and depth of cut, which came closest to the quality of the shaved surfaces. An increase in the cutting depth generally increased the core surface roughness and fuzziness, for both tools, and this trend increased with an increase in the stepover value. The species-dependent machining quality implies that the selection of tool geometry and process parameters must be tailored per species. Full article

Innovating seal structures and optimizing size parameters are effective ways to enhance the leakage characteristics of labyrinth seals (LSs). Inspired by the ecological fishways with high flow resistance on dam sides, a novel bio-inspired staggered labyrinth seal is proposed. The leakage characteristics of both the curved-edged bio-inspired labyrinth seal (CELS) and the straight-edged bio-inspired labyrinth seal (SELS) at different tooth-incline angles are studied numerically and experimentally. The influence of key geometrical parameters on the leakage characteristics and flow field parameters of the CELSs are investigated, and the leakage control mechanism of bio-inspired LSs is revealed via analyzing flow field parameter distribution. The results indicate that, compared to conventional double-sided staggered straight-tooth labyrinth seals, the leakage rate reduction in CELSs is up to 30% when the incline angle is equal to 25°, outperforming that of the SELS in leakage control. This improvement is mainly attributed to the flow path bending and jet contraction effects at the tooth-tip entrance, along with the thermodynamic effects of the high-turbulence dissipation zone adjacent to the tooth top. The optimum leakage characteristics can be achieved when seal clearance h < 0.5 mm, aspect ratio δ < 0.6, and tooth thickness t < 1.5 mm. This work provides new insights into the structural design of high-resistance and low-leakage labyrinth seals. Full article

Owing to its enhanced production efficiency, roller hemming has become the mainstream process for forming and joining metal sheets in the automotive industry. This study investigates the roller hemming process of a specific car door panel through a combination of experimental analysis and finite element analysis (FEA) on both straight-edge and curved-edge flat surfaces. Consequently, the mechanical properties of the door panel, including tensile strength, yield strength, modulus of elasticity, and Poisson’s ratio, were estimated through tensile testing and then underwent finite element modeling. The simulation results demonstrated the varying distribution of stress during the rolling hemming process, with the highest stress concentration observed in the bending area. Additionally, creepage and growing results were acquired from both simulation and experimental data to validate the precision of the numerical model. A comparison was made between the experimental and simulation results of the external forces exerted by the roller on the panel. In both straight- and curved-edge sections, the external force during final hemming exceeded that during pre-hemming, as revealed by experimental measurements of both normal and tangential external forces, surpassing their corresponding simulated values. Full article

To overcome the shortcomings of plowing and rotary tillage, a human-like weeding shoveling machine was designed. The machine’s various moving rods were analyzed using Matlab R2019b(9.7.0.1190202) software to determine the appropriate entry and cutting conditions, as well as non-cutting conditions. It was concluded that a θ2 of 90° was optimal for cutting the soil and that the shoveling depth was suitable for greenhouse weeding. The Adams and DEM coupled discrete element simulation system was developed for this machine and was used to analyze the rotating shaft torque and shovel bending moment. A strain measurement system based on strain gauges was designed to measure the rotating shaft torque and shovel bar bending moment. A bending moment and torque measurement system was designed to perform field measurement tests for comparison with simulation results. The simulation system’s rotating shaft had an average torque error of 6.26%, while the shovel rod’s bending moment had an average error of 5.43%. The simulation accuracy was within the acceptable error range. Table U8 (81 × 44) of the Uniform Design of the Mixing Factor Level for the Homogeneous Virtual Simulation Test includes eight levels of forward machine speed ranging from 0.1 to 0.45 m/s and four levels of output shaft speed ranging from 90 to 165 r/min. Crank lengths were set at four levels ranging from 155 to 185 mm, while shovel lengths were set at four levels ranging from 185 to 230 mm. Four types of shovel shapes were proposed, including pointed curved shovels, pointed straight shovels, straight-edged curved shovels, and straight-edged straight shovels. A mathematical model was created via a regression analysis of the results of coupled simulation tests to establish the relationship between shaft torque and shovel rod bending moment, tool advance speed, shaft speed, crank length, tool length, and tool shape. The model was used to determine the optimum working parameters. Full article

This two-part manuscript presents a comprehensive methodology for the irregularity assessment of urban stone pavements. The proper road surface assessment using key performance indicators is necessary to plan appropriate maintenance strategies. However, there are no monitoring methods or evaluation criteria for stone pavements whose surfaces are more uneven than traditional ones due to their structural characteristics. Therefore, it is useful to define criteria for assessing irregularities considering the comfort experienced by road users and classify their conditions. This second part presents the geometric and comfort analyses of 40 urban branch profiles to describe pavement unevenness. In particular, four methods have been investigated: the International Roughness Index (IRI) according to ASTM E1926, the surface profile classification according to ISO 8608, the comfort index (a_wz) according to ISO 2631, and the straightedge analysis for stone pavements (SASP) proposed by the authors that is able to evaluate the effect of localized irregularities, taking into account different urban vehicles. In conclusion, four classes have been defined to describe geometric and comfort conditions that can support road manager decisions in order to implement an effective pavement management system. Full article

Stone pavements are the historical, architectural, and cultural heritage of lots of cities in Italy and the world. Road managers should be able to make decisions on the global conditions to define the most suitable strategies and maintenance interventions for every type of pavement. There are no standard monitoring methods or criteria for evaluating stone pavement performance. These pavements have more uneven surfaces than traditional pavements, but this characteristic could be accepted if type of vehicles and relative travel conditions are considered. Therefore, it is useful to define criteria for assessing roughness considering the comfort experienced by users in different vehicles. In this research, both traditional and innovative methodologies for assessing irregularities have been investigated using true stone surface profiles. In this regard, traditional performance indicators such as the International Roughness Index (IRI) defined by the ASTM E1926, the ISO 8608 classification, and the frequency-weighted vertical acceleration (a_wz) provided by ISO 2631-1 for comfort assessment have been considered. In the case of comfort assessment, three dynamic vehicle models (bike, automobile, and bus) have been adopted. Finally, this two-part paper also proposes an innovative straightedge analysis for stone pavements (SASP) to evaluate the effect on traffic of both pavement profile roughness and localized irregularities. In this way, the authors aim to provide an effective tool to monitor stone pavements. Full article

The core of the ultrasonic machining system is the acoustic vibration component. Due to the inconsistency of the assembly conditions between the junction surfaces of the acoustic vibration component, the resonant frequency of the ultrasonic acoustic vibration component after the size adjustment of the ultrasonic horn is low, and the Impedance mismatch occurs in the ultrasonic system. In this paper, considering the influence of assembly conditions, the optimal assembly parameters were studied to reduce the junction surface’s influence on the ultra-sonic horn’s performance parameters. The paper analyzed the assembly structure, assembly parameters, and static and dynamic performance parameters of the acoustic vibration components and established a static and dynamic performance parameter measurement system. The assembly parameters of the ultrasonic acoustic vibration components were analyzed and determined. The static performance parameters of the ultrasonic acoustic components were measured and analyzed for the assembly parameters of the junction surface at the ultrasonic horn and the straight-edged knife. The optimal assembly parameters were preliminarily determined based on the analysis of the static performance parameters. The optimal assembly parameters of the junction surface of the ultrasonic horn and the straight-edged knife were determined through the measurement and analysis of the dynamic performance parameters of the two junction surfaces. The work is the basis for the adjustment of the ultrasonic horn. It also provides a basis for improving the working performance, manufacturing precision, and production efficiency of the ultrasonic horn while further popularizing the application of ultrasonic processing. Full article

A Circulating Water Channel (CWC) is an important piece of equipment for hydrodynamic tests in ocean engineering, the quality of the flow field produced by the CWC directly affects the accuracy of the experimental results. Optimizing the key parts of the CWC device can efficiently improve the velocity uniformity and helps to achieve a high-level flow performance. In this paper, a CWC flume is set up numerically, and a series of hydrodynamic tests were carried out to evaluate the flow uniformity by optimizing the turning vane and contraction section. The numerical model is solved based on the RANS equation by using the RNG model to simulate turbulence. The improved design of the CWC includes the investigations of the flow guiding vane at the turning corners and the contraction section in the flow acceleration zone. The turning vane cross-sectional shape, the straight-edged length of the wing, and the layout of the contraction transition section design were considered and verified. The obtained results show that the wing-type turning vane with appropriate straight-edged length can help to improve the velocity uniformity of the flow field. The Witozinsky transition curve could achieve better pressure gradient effects for CWC contraction section design, and the flow uniformity improved by increasing the contraction transition length. Based on the optimal design, the internal flow characteristics of the circulating water channel have been greatly improved, laying a solid foundation for wind-wave-current multifunction CWC equipment applications for future experiments. Full article

Gravel pavement has lower construction costs but poorer performance than asphalt surfaces on roads. It also emits dust and deforms under the impact of vehicle loads and ambient air factors; the resulting ripples and ruts constantly deepen, and therefore increase vehicle vibrations and fuel consumption, and reduce safe driving speed and comfort. In this study, existing pavement quality evaluation indexes are analysed, and a methodology for adapting them for roads with gravel pavement is proposed. We report the measured wave depth and length of gravel pavement profile using the straightedge method on a 160 m long road section at three stages of road utilization. The measured pavement elevation was processed according to ISO 8608, and the frequency response of a vehicle was investigated using simulations in MATLAB/Simulink. The international roughness index (IRI) analysis showed that a speed of 30–45 km/h instead of 80 km/h provided the objective results of the IRI calculation on the flexible pavement due to the decreasing velocity of a vehicle’s unsprung mass on a more deteriorated road pavement state. The influence of the corrugation phenomenon of gravel pavement was explored, identifying specific driving safety and comfort cases. Finally, an increase in the dynamic load coefficient (DLC) at a low speed of 30 km/h on the most deteriorated pavement and a high speed of 90 km/h on the middle-quality pavement demonstrated the demand for timely gravel pavement maintenance and the complicated prediction of a safe driving speed for drivers. The main relevant objectives of this study are the adaptation of a road roughness indicator to gravel pavement, including the evaluation of vehicle dynamic responses at different speeds and pavement deterioration states. Full article

The fracture of a flat-surface straight-edge hemmed component of aluminum alloy sheets was investigated in this study. The specimen was made of 1 mm thick 6014-T4. Natural aging characteristics of 6014-T4 were studied via uniaxial tensile tests. The results show that the yield stress and ultimate tensile strength increased while the uniform elongation, strain hardening exponent, and plastic strain ratio decreased during the natural aging period, which worsened the formability. The sheet was biaxially stretched to obtain a pre-strain before the flanging and hemming operation. The influence of the flanging radius on the fracture was evaluated using experimental and numerical methods, and the optimum values were obtained. The comparison between the roller hemming and die hemming process proved that the former tends to produce better formability. Full article