Search Results (247)

For a two-stage variable-pitch axial fan, a perforation design in first-stage rotor blades was proposed to improve aerodynamic performance and reduce acoustic noise. Utilizing steady-state simulations in Fluent, the internal flow characteristics of the fan before and after perforation were studied, and the changes in noise and vortex structure were examined by the large eddy simulation. Additionally, the perforation diameter with better performance was applied to the second-stage rotor blades and both first- and second-stage rotor blades, and the effects of perforation on blades of different stages were compared. The results show that an appropriate perforation diameter can improve the performance of the fan. Considering the changes in total pressure rise and efficiency, d = 6 mm is the preferable choice. Proper perforation diameter has a significant effect on noise suppression, and the noise-reduction effect is more pronounced in the high-frequency range. Among the models, d = 10 mm shows the best noise-reduction effect. At this perforation diameter, the vortex at the trailing edge of the rotor blades forms a regular ring-like vortex chain, resulting in lower noise levels. Perforation in the first-stage rotor blade can enhance the fan’s performance, while perforation in the second-stage rotor blades leads to a decrease in performance. Additionally, perforation can effectively reduce the noise at each stage. Considering both performance and noise variations, the preferable perforation scheme is simultaneous perforating in the first- and second-stage rotor blades with a perforation diameter of 10 mm. Full article

In this study, we propose an optimized shield gate trench 4H-SiC structure with effective gate oxide protection. The proposed device has a split trench with a P+ shield region, and the P+ shield is grounded by the middle deep trench. Our simulation results show that the peak electric field near the gate oxide is almost completely suppressed. Compared with a conventional P+ shield device, our proposed structure achieves a 78% reduction in the Q_gd and a 108% increase in the FoM (figure of merit) simultaneously. Additionally, it is estimated that the device cell pitch can be reduced to 1.8 μm with a R_on below 0.94 mΩ·cm², in theory. These demonstrated device performance metrics, as well as its simple structure and good compatibility, make our proposed SiC MOSFET highly attractive for future high-performance applications. Full article

In hub-motor electric vehicles (HMEVs), performance is adversely affected by the mechanical-electromagnetic coupling effect arising from deformations of the air gap in the Permanent Magnet Brushless Direct Current Motor (PM BLDC), which are exacerbated by varying road conditions. In this paper, a Model Predictive Control (MPC) strategy for HMEVs equipped with air suspension (AS) is introduced to enhance ride comfort. Firstly, an 18-degree of freedom (DOF) full-vehicle model incorporating unbalanced electromagnetic forces (UEMFs) induced by motor eccentricities is developed and experimentally validated. Additionally, a Minimum Model Error Extended Kalman Filter (MME-EKF) observer is designed to estimate unmeasurable state variables and account for errors resulting from sprung mass variations. To further improve vehicle performance, the MPC optimization objective is formulated by considering the suspension damping force and dynamic displacement constraints, solving for the optimal suspension force within a rolling time domain. Simulation results demonstrate that the proposed MPC approach significantly improves ride comfort, effectively mitigates coupling effects in hub driving motors, and ensures that suspension dynamic stroke adheres to safety criteria. Comparative analyses indicate that the MPC controller outperforms conventional PID control, achieving substantial reductions of approximately 41.59% in sprung mass vertical acceleration, 14.29% in motor eccentricity, 1.78% in tire dynamic load, 17.65% in roll angular acceleration, and 16.67% in pitch angular acceleration. Full article

In wind turbine systems, bolted connections in pitch bearings are subjected to working loads that reduce bolt preload. This reduction can lead to issues such as bolt loosening and eccentric loading, which in turn results in the nonuniform distribution of contact stress across joint surfaces. These issues can compromise structural integrity and reduce fatigue life. However, the study of contact stress mainly focuses on theoretical research, lacking relatively large, complex structures. Also, the stress testing methods for contact surfaces of bolted connections are limited in practical engineering. In this paper, a localized bolt connection model using the finite element method according to pitch bearings in wind turbine systems was established. The contact stress distribution patterns of bolt specimens under varying preloads were investigated. Comparative numerical simulation and experimental analysis using thin-film pressure sensors were conducted. Furthermore, the effect of bolt assembly in different tightening processes on the contours of contact stress was analyzed to identify the optimal tightening sequence. The experimental results demonstrate a positive correlation between preload and maximum contact stress, with stress distribution exhibiting symmetry around the bolt hole and decreasing radially outward. Thin-film pressure sensors can be used for contact stress detection. Furthermore, the diagonal tightening method can achieve a more uniform contact stress distribution compared to other methods, such as sequential and alternate tightening. The findings provide valuable insights for optimizing the contact stress distribution and tightening processes in bolted joint assemblies. Full article

To address the weak adaptability of the passive X-type interconnection hydropneumatic suspension to different road surfaces and the poor performance of traditional single-control methods, an active controller based on the extended state observer (ESO) and model predictive control (MPC) was designed for the X-type interconnection hydropneumatic suspension of heavy-duty special vehicles. First, the structure of the X-type interconnection hydropneumatic suspension was analyzed. A three-degree-of-freedom (DOF) linearized hydropneumatic suspension model with disturbances was established based of the seven-DOF full-vehicle model of the active X-type interconnection hydropneumatic suspension. The disturbances were analyzed, and a disturbance ESO was developed. A controller for MPC was subsequently designed based on the linearized state space model, forming a controller for ESO-MPC. Simulations were conducted on both C-class random roads and convex pavement, with fuzzy PID control included for comparison. The simulation results demonstrated that, compared with the passive X-type interconnection hydropneumatic suspension, the active suspension with the controller for ESO-MPC achieved reductions in body vertical acceleration, pitch angular acceleration, and roll angular acceleration of 18.7%, 24.7%, and 26.1%, respectively, on Class C random roads. With fuzzy PID control, the reductions were 5.59%, 7.99%, and 15.54%, respectively. For convex pavement, the controller for ESO-MPC reduced body vertical acceleration, pitch angular acceleration, and roll angular acceleration by 36.5%, 21.2%, and 18.1%, respectively, whereas fuzzy PID control resulted in reductions of 14.04%, 10.6%, and 7.92%, respectively. Compared with fuzzy PID control, the controller for ESO-MPC significantly improved the performance of the hydropneumatic suspension system, achieving precise control of the X-type interconnection hydropneumatic suspension system for heavy-duty special vehicles, thereby enhancing ride comfort and stability. Full article

Due to the limitations of wind tunnel speed and size, achieving a model’s Reynolds number equal to the actual Reynolds number is challenging and may lead to discrepancies between experimental and actual results. To investigate the effects of the Reynolds number on the aerodynamic forces and vortex-induced vibration (VIV) characteristics of a streamlined box girder, wind tunnel tests were conducted to study the variations in aerodynamic forces and surface pressures on the static main beam, as well as the VIV response and time–frequency characteristics of the aerodynamic forces on the dynamic main beam, as the Reynolds number varied. The results indicate that in static tests, as the Reynolds number increases, the drag coefficient of the main beam decreases, the lift coefficient slightly increases, and the pitching moment coefficient remains almost unchanged. The root mean square (RMS) values of the wind pressure coefficients show a significant Reynolds number effect, with values generally decreasing as the Reynolds number increases. In free vibration tests, as the Reynolds number increases, the onset wind speed of VIV increases from 14.35 m/s to 16.03 m/s, the maximum amplitude decreases from 0.076 to 0.004, and the VIV lock-in range narrows. The dynamic pressure results indicate that as the Reynolds number increases, the RMS values of the wind pressure coefficients decrease. At some measurement points, the dominant frequencies of the fluctuating pressure amplitude spectra deviate from the corresponding VIV frequency, and the correlation and contribution coefficients between the local aerodynamic forces and the overall vortex-induced force (VIF) decrease. These changes may explain the reduction in the VIV amplitude with an increasing Reynolds number. The motion state of the main beam has a minimal effect on the mean wind pressure coefficients and their Reynolds number effect, whereas it has a more significant effect on the RMS values of the pressure coefficients. Full article

We investigated the orthogonal cutting process by using machine learning models to predict its performance. This study used the AZ91 magnesium alloy as the workpiece material, and machining was performed under the Minimum Quantity Lubrication (MQL) technique. The input parameters were the feed, cutting speed and MQL flow rate. Additionally, the outputs were flank tool wear, the chip contact length, peak distance, valley distance, pitch distance, chip segmentation ratio, compression ratio and shear angle. Studies on machine learning (ML) models being employed to evaluate the performance of the MQL-assisted orthogonal machining of AZ91 are very rarely found in the literature. This study explored machine learning (ML) as a data-driven alternative, evaluating decision tree regression, Bayesian Optimization, Random Forest Regression and XGBoost for predicting machinability. A comprehensive dataset of the cutting parameters and outcomes was utilized to train and validate these models, aiming to enhance the accuracy of the predictive analysis. The performance of each model was evaluated based on error metrics such as the mean squared error (MSE) and R-squared values. Among these models, XGBoost demonstrated a superior predictive accuracy, outperforming the other methods in terms of its precision and generalizability. These findings suggest that XGBoost provides a more robust solution for modeling the complexities of the orthogonal cutting process, offering valuable insights into process optimization. The analysis supports that the XGBoost model is the most accurate, with a 34.1% reduction in the mean squared error and a 17.1% reduction in the mean absolute error over these values for the Decision Tree. It also outperforms the Random Forest Regression model, achieving a 19.8% decrease in the mean squared error and a 7.1% decrease in the mean absolute error. Full article

Wind power output fluctuations, driven by variable wind speeds, create significant challenges for grid stability and the efficient use of wind turbines, particularly in high-wind-penetration areas. This study proposes a combined approach utilizing an ultra-capacitor energy storage system and fuzzy-control-based pitch angle adjustment to address these challenges. The fuzzy control system dynamically responds to wind speed variations, optimizing energy capture while minimizing mechanical stress on turbine components, and the ultra-capacitor provides instantaneous buffering of power surpluses and deficits. Simulations conducted on a 50 kW DFIG wind turbine powering a 23 kW load demonstrated a substantial reduction in power fluctuations by a factor of 3.747, decreasing the power fluctuation reduction scale from 13.04% to 3.48%. These results highlight the effectiveness of the proposed system in improving the stability, reliability, and quality of wind energy, thereby advancing the broader adoption of renewable energy and contributing to sustainable energy solutions. Full article

This paper presents the design of an electric amphibious vehicle with buoyancy provided by inflatable pontoons, referred to as the Electric Inflatable Pontoon amphibious vehicle (E-IPAMV). To investigate the effect of pontoon arrangements on resistance performance, maneuverability, seakeeping, transverse stability, and longitudinal stability of E-IPAMV, STAR-CCM+ and Maxsurf are used to solve the above performance parameters. A constrained space Latin hypercube experimental design is employed, using the lengths of the inflatable pontoons at five installation positions as input variables, and total resistance, steady turning diameter, maximum pitch angle, transverse metacentric height, and longitudinal metacentric height as output variables. A neural network model is then established and validated. Based on this model, NSGA-II is employed to optimize the pontoon lengths at the five installation positions, yielding Pareto-optimal solutions. Finally, considering project and manufacturing requirements, two optimized design schemes are proposed. Compared to the original design, optimization scheme 1 shows a slight reduction in seakeeping but improvements in other hydrodynamic performances. Meanwhile, optimization scheme 2 enhances all hydrodynamic performances. Specifically, in optimization scheme 2, maneuverability increases by the smallest amount, showing 23.43% improvement compared to the original design, while transverse stability sees the greatest improvement, increasing by 290.99% compared to the original design. Full article

A wafer-scale process for fabricating monolithically suspended nano-perforated membranes (NPMs) with integrated support structures into silicon is developed. Existing fabrication methods are suitable for many desired geometries, but face challenges related to mechanical robustness and fabrication complexity. We demonstrate a process that utilizes the cyclic deposit, remove, etch, and multi-step (DREM) process for directional etching of high-aspect-ratio (HAR) 300 nm in diameter nano-pores of 700 nm pitch. Subsequently, a buried cavity beneath the nano-pores is formed by switching to an isotropic etch, which effectively yields a thick NPM. Due to this architecture’s flexibility and process robustness, structural parameters such as membrane thickness, diameter, integrated support structures, and cavity height can be adjusted, allowing a wide range of NPM geometries. This work presents NPMs with final thicknesses of 4.5 µm, 6.5 µm, and 12 µm. Detailed steps of this new approach are discussed, including the etching of a through-silicon-via to establish the connection of the NPM to the macro-world. Our approach to fabricating NPMs within single-crystal silicon overcomes some of the limitations of previous methods. Owing to its monolithic design, this NPM architecture permits further enhancements through material deposition, pore size reduction, and surface functionalization, broadening its application potential for corrosive environments, purification and separation processes, and numerous other advanced applications. Full article

An experimental investigation was carried out to understand the effects of LEP (leading-edge protuberance) blades on the structural characteristics of VAWTs. A series of experiments were performed on VAWTs with straight and LEP blades for a wide range of wind velocity (6 m/s to 20 m/s) and pitch angles (−20° to 20°), and the structural excitations on the VAWT structure were measured using a triaxial accelerometer in each case. The raw acceleration data were extensively processed in the time and frequency domains to identify the variation in structural excitation caused by the unsteady wind and aerodynamic loads on the VAWT structure. Understanding the aerodynamic changes and their impact on structural characteristics is essential. The current study examines how LEP influences the structural excitation of VAWTs. However, a great deal of aerodynamic variation was observed for the LEP blades, so the straight blades of the VAWT were replaced with various modified LEP blades, for which a similar set of experiments was carried out. The study presents a better performance (self-starting, stall-mitigating) for VAWTs with LEP 3 and 2 blades, with a significant reduction in the excitation of loads due to wind load and the changes in aerodynamics observed in the along- and across-wind directions. Full article

Our study considered porous Bouligand structured polymer, comprising polymer fibres with porous spaces between them. These are more complicated structures than the non-porous Bouligand, since the addition of porosity into the material creates a secondary variable besides fibre pitch. There is currently no analytical model available to predict the modulus of such materials. Our paper explores the correlation between porosity, polymer fibre pitch angle, and flexural modulus in porous Bouligand structured polymers. Our structures were digitally manufactured using stereolithography (SLA) additive manufacturing methods, after which they were subjected to three-point bending tests. Our aim was to simply and parametrically develop an analytical model that would capture the influences of both porosity and polymer fibre pitch angle on the flexural modulus of the material. Our model is expressed as $E_f=E_{poro}(a{\theta }_f^3+b{\theta }_f^2+c{\theta }_f+d)$, and we derive this by applying non-linear regression to our experimental data. This model predicts the flexural modulus, $E_f$, of porous Bouligand structured polymer as a function of both porosity and pitch angle. Here, $E_{poro}$ is defined as the solid material modulus, $E_{solid}$, multiplied by porosity, $\varphi$ and is a linear reduction in the modulus as a function of increasing porosity, while ${\theta }_f$ signifies the polymer fibre pitch angle. This relationship is relatively accurate within the range of 10° ≤ θ_f ≤ 50°, and for porosity values ranging from $0.277\le 0.356$, as supported by our evidence to date. Full article

Background/Objectives: Three-dimensional motion analysis is often used to evaluate improvements or decrements in movement patterns in athletes. The purpose of this study was to evaluate the reliability of joint flexion/extension angles of the pitching elbow and bilateral knees and hips in softball pitchers. Methods: Fourteen softball pitchers (17.9 ± 2.3 years) were tested in one session consisting of four sets of five consecutive fastballs and a second session of two sets of five fastballs. The magnitude of systematic bias and within-subject variation was calculated between pitches. An iterative intraclass correlation coefficient (ICC) process was used to determine intra- and inter-session reliability, standard error of measurement and minimal detectable change. Results: Reductions in within-subject variation were observed for all variables when the number of pitches used in calculations was increased. Intra-session ICC values ranged from an average of 0.643 for pitching elbow to 0.989 for stride leg knee. Inter-session ICC values ranged from an average of 0.663 for pitching elbow to 0.996 for stride leg knee. Conclusions: Joint flexion/extension angles during the softball windmill pitch can be measured with good to high reliability using three-dimensional motion analysis. Biomechanical analysis can be confidently used to detect changes in the pitching motion over the course of a season or following an intervention. Full article

In this study, a composite control algorithm based on classical control methods is developed to achieve all control objectives, such as power production, load reduction, and motion reduction, for the floating wind turbine. In previous studies, peak shaving and nacelle feedback were used together to reduce both platform motion and the tower-base loads of floating wind turbines. The new approach presented in this study not only addresses the platform motion and tower loads but also aims to mitigate the rotor speed fluctuations and the blade loads by additionally introducing feedforward control and individual pitch control. This expansion enhances the applicability and control performance of classical control algorithms. To achieve this, parametric simulations were conducted using OpenFAST to assess the effects of control parameter variations for each control technique. The simulation results showed that the proposed control algorithm significantly reduced the rotor speed fluctuations, tower loads, blade loads, and platform motion compared with the baseline controller. Full article

This study presents the development and comparative analysis of a new Y-type floating offshore wind turbine platform based on the existing T-type model. Utilizing advanced simulation tools, such as MSC, Patran and Nastran 2022.3, FEGate For Ship 5.0, and Ansys AQWA 2021 R2, extensive evaluations are conducted on the structural strength, stability, and dynamic response of both the T-type and the newly proposed Y-type platforms. In this research, the structural optimization algorithm based on the above simulation tools is adopted, and its results are compared with preoptimization results to demonstrate the improvements made in design precision and reliability. Results indicate that the Y-type model achieves a maximum reduction in von Mises stress by 30.21 MPa compared to the T-type model, and its heave and pitch motion amplitudes are reduced by 4.3412 m and 4.9362°, respectively, under extreme sea state conditions. Through structural optimization using the Nastran SOL200 module, the column structure weight is reduced by 11.31%, meeting the strength requirements while enhancing efficiency. These findings highlight the Y-type platform’s improved performance and provide robust design strategies for floating offshore wind turbines in deep-water regions, crucial for advancing global renewable energy solutions. Future research should focus on the impacts of different marine conditions on platform performance and consider integrating new materials or innovative design enhancements to further optimize platform functionality. Additionally, due to potential limitations from model simplification, emphasis on real-world testing and validation under operational conditions is recommended. Overall, this research clarifies the differences in structural performance between the T-type and Y-type floating platforms and introduces an improved platform design approach, offering valuable insights and guidance for the future development of floating offshore wind turbine technology. Full article