Search Results (3,894)

High penetration of wind farms into the power grid lowers system inertia and compromises stability. This paper proposes a grid-forming control strategy for Permanent Magnet Synchronous Generator (PMSG) wind turbines based on DC-link voltage matching and virtual inertia. First, a relationship between grid frequency and DC-link voltage is established, replacing the need for a phase-locked loop. Then, DC voltage dynamics are utilized to trigger a real-time switching of the power tracking curve, releasing the rotor’s kinetic energy for inertia response. This is further coordinated with a de-loading control that maintains active power reserves through over-speeding or pitch control. Finally, the MATLAB/Simulink simulation results and RT-LAB hardware-in-the-loop experiments demonstrate the capability of the proposed control strategy to provide rapid active power support during grid disturbances. Full article

In racing cars, a low ride height is crucial for inverted wings and ground-effect systems to function effectively, significantly enhancing aerodynamic performance but also increasing sensitivity to pitch and roll variations. However, the specific impact of wheel-ground conditions on racing cars under ride-height-related attitude variations has not received attention. This study employed numerical simulations (compared with wind tunnel test data) to investigate these effects on racecar aerodynamic characteristics, analyzing three specific wheel-ground combinations: moving ground with rotating wheels (MR), moving ground with stationary wheels (MS), and stationary ground with stationary wheels (SS). A systematic analysis was conducted on aerodynamic changes associated with wheel-plane total pressure coefficient differences, upper-lower surface pressure coefficient variations, and front-rear axle aerodynamic force distributions, elucidating individual component contributions to overall performance changes induced by wheel-ground alterations. Results indicate that wheel conditions, especially rear wheels and their localized interactions with the diffuser-equipped body predominantly influence drag. In contrast, ground conditions primarily affect the body and front wing to alter downforce, with induced drag variations further amplifying total drag differences. Moreover, ground conditions’ impact on the front wing is modulated by vehicle attitude, resulting in either increased or decreased front wing downforce and thus altering aerodynamic balance. These insights highlight that ride-height related attitudes are critical variables when evaluating combined wheel-ground effects, and while wheel rotation is significant, the aerodynamic force and balance changes induced by ground conditions (as modulated by attitude) warrant greater attention. This understanding provides valuable guidance for racecar aerodynamic design. Full article

The use of ships and boats as sea-state (SS) measurement platforms has the potential to expand ocean observations while providing actionable information for real-time operational decision-making at sea. Within the framework of the Wave Buoy Analogy (WBA), this work develops an inverse approach in which efficient simulations of wave-induced motions of an advancing vessel are used to train a neural network (NN) to predict SS parameters across a broad range of wave climates. We show that a reduced set of novel motion discriminant variables (MDVs)—computed from short time series of heave, roll, and pitch motions measured by an onboard inertial measurement unit (IMU), together with the vessel’s forward speed—provides sufficient and robust information for accurate, near-real-time SS estimation. The methodology targets small, barge-like tugboats whose operations are SS-limited and whose motions can become large and strongly nonlinear near their upper operating limits. To accurately model such responses and generate training data, an efficient nonlinear time-domain seakeeping model is developed that includes nonlinear hydrostatic and viscous damping terms and explicitly accounts for forward-speed effects. The model is experimentally validated using a scaled physical model in laboratory wave-tank tests, demonstrating the necessity of these nonlinear contributions for this class of vessels. The validated model is then used to generate large, high-fidelity datasets for NN training. When applied to independent numerically simulated motion time series, the trained NN predicts SS parameters with errors typically below 5%, with slightly larger errors for SS directionality under relatively high measurement noise. Application to experimentally measured vessel motions yields similarly small errors, confirming the robustness and practical applicability of the proposed framework. In operational settings, the trained NN can be deployed onboard a tugboat and driven by IMU measurements to provide real-time SS estimates. While results are presented for a specific vessel, the methodology is general and readily transferable to other ship geometries given appropriate hydrodynamic coefficients. Full article

To address the complex surface curvature, massive dimensions, and variable pitch angles of wind turbine blades, this paper proposes a climbing robot design based on a variable-cell mechanism. By dynamically adjusting the support span and body posture, the robot adapts to the geometric features of different blade regions, enabling stable and efficient non-destructive inspection operations. Two reconfigurable configurations—a planar quadrilateral and a regular hexagon—are proposed based on the geometric characteristics of different blade regions. The configuration switching conditions and multi-leg cooperative control mechanisms are investigated. Through static stability margin analysis, the stable gait space and maximum stride length for each configuration are determined, optimizing the robot’s motion performance on surfaces with varying curvature. Simulation and experimental results demonstrate that the proposed multi-configuration gait planning strategy exhibits excellent adaptability and climbing stability across segments of varying curvature. This provides a theoretical foundation and methodological support for the engineering application of robots in wind turbine blade maintenance. Full article

This paper addresses Region-3 control of a 2.5 MW three-bladed HAWT using a data-driven workflow that links empirical modeling to implementable pitch control. To focus on fundamental regulation dynamics, the turbine is modeled as a rigid single-mass drivetrain driven by identified quasi-steady aerodynamics. First, we identify a compact shaft-power surface $P(\omega ,V,\beta )$ and recover the associated MPP condition, which clarifies why the optimal rotor speed rises with wind and motivates a comparison between capped-MPP operation and constant-speed regulation. We then synthesize a practical Region-3 loop—PI in rate with a first-order pitch servo and saturation handling—and evaluate proportional (P), PI, and PI + servo controllers under sinusoidal and Kaimal-turbulent inflow. Finally, we propose an adaptive PI variant that keeps a fixed acceleration feed-through but retunes the integral path online via ARX(1,1) + RLS to maintain a target closed-loop bandwidth. Performance metrics computed over the full simulation window (t ∈ [0, 50] s) show that P-only control exhibits large steady bias and cap violations; PI recenters speed and power around their targets; adding a pitch servo further trims peaks and ripple. In steady-state turbulent tests, PI + servo achieves tight regulation, Δω_peak ≈ 0.033% (0.079 rad/s), P_RMS ≈ 0.62%, while the adaptive PI maintains similar tightness with the lowest variability overall Δω_peak ≈ 0.0104% (0.025 rad/s), P_RMS ≈ 0.17. The workflow yields a practically implementable β(V) schedule and a lightweight adaptation mechanism that compensates for slow aerodynamic performance drift without changing the control structure. While structural loads and aeroelastic modes are not explicitly modeled, the proposed controller enforces strict speed and power constraints via a rigid-body dynamic analysis. Extensions to IPC, preview/forecast augmentation, and validation on higher-fidelity aeroelastic/drivetrain models are identified as future work. Full article

The trend toward sustainable protein substitutes is driven by growing concerns about food security, sustainability, and human health. Spent brewer’s yeast and wine lees are two by-products of the beer and wine industry with high potential, owing to their complex composition, which remains insufficiently exploited. The purpose of this study was to perform a comparative analysis of the two by-products under two different drying techniques to observe if there are significant changes in composition: oven-drying and freeze-drying. Two samples of wine lees from producers in the Republic of Moldova were used—Asconi Winery and Cricova Winery (Republic of Moldova)—as well as a sample of spent brewer’s yeast offered by Efes Vitanta Moldova Brewery. The samples were characterized in terms of physicochemical properties, antioxidant activity (total polyphenol content (TPC), individual polyphenol content, and DPPH assay scavenging activity), color, mineral content, structural composition (FT-IR analysis), and microstructure, as well as organic acid and B vitamin content. The highest protein content was recorded in the samples from Cricova (45.35–46.81%). Regarding the polyphenols, the oven-dried Efes sample exhibited a TPC value of 3.98 mg GAE/g, while the highest DPPH value of 88.92% was observed in the Asconi sample. All analyzed samples showed a diverse composition of individual phenolic compounds, including 4-hydroxybenzoic acid, vanillic acid, caffeic acid, and rosmarinic acid. Wine lees samples have the highest content of B vitamins, with vitamin B3 being the most abundant across all samples, followed by vitamin B6. The microstructural examination revealed autolyzed yeast cells, with more permeable cell walls, favorable to subsequent valorization treatments, and in some cases, cells form clusters in a mother-daughter junction due to serial re-pitching. Full article

Aiming to address the problems of the violent fluctuation of winch traction rope and tire forces and the high safety risk caused by coupling ship motions (rolling, pitching, and heaving), wind loads, and deck space limitations in carrier-based aircraft, this paper focuses on a multi-winch traction system on a small deck. A fully coupled dynamic model of an aircraft landing gear–tire–rope–winch system is constructed, ADAMS2020 and MATLAB/Simulink (MATLAB R2021b) co-simulations are used to develop the three-winch and five-winch traction system models, and a Fiala tire model and a telescopic landing gear model are adopted to build a precise mechanical model of the aircraft. The PID control strategy is proposed, based on the Bessel curve, to control the driving trajectory of the aircraft, and the quantitative influence of ship motion, winch number, and preset trajectory on traction dynamic characteristics is systematically studied. Compared to without trajectory control, the peak force of the winch rope before the start-up phase of the three-winch system is reduced by 54.9%, and the five-winch system is reduced by 57.6%. The fluctuation amplitude of the lateral force of the rear wheel is greater than that of the front wheel, up to a maximum of 215% of the front wheel. The correlation coefficient between the theoretical model and the simulation results is 0.91~0.97, and the error is less than 12%. The PID control strategy based on the Bessel trajectory can significantly improve the steadiness and security of the carrier-based aircraft winch traction system on a small deck. The study delivers the requisite theory and engineering means for the optimized design of carrier-based aircraft traction systems. Full article

Background/Objectives: The purpose of this study was to evaluate the reliability and diagnostic accuracy of smartphone-based photogrammetry for the assessment of pes planus and to determine its agreement with standard radiographic measurements. Methods: This prospective diagnostic study included 100 skeletally mature patients (50 males, 50 females; mean age 43.4 years) who underwent standardized lateral weight-bearing foot radiographs and smartphone-based foot photography. The calcaneal pitch angle (CPA) was measured on radiographs, and a corresponding photographic arch pitch angle (P-APA) was measured from standardized smartphone photographs using digital software (Angle Meter iOS v1.9.8). Three independent observers performed each measurement twice. Inter- and intra-observer reliability was assessed using intraclass correlation coefficients (ICC). Agreement between methods was evaluated with Pearson correlation, Lin’s concordance correlation coefficient (CCC), Bland–Altman analysis, and Deming regression. Receiver operating characteristic (ROC) analysis was performed to determine the diagnostic accuracy of calibrated P-APA, with the radiographic threshold of 18° serving as the reference standard for pes planus classification. Results: All measurements demonstrated excellent intra- and inter-observer reliability (ICC ≥ 0.900). P-APA values were systematically higher than radiographic values (31.8° ± 4.3 vs. 21.8° ± 5.5; p < 0.001). A strong correlation was observed between the two methods (r = 0.799, p < 0.001), but concordance was poor (CCC = 0.222). Bland–Altman analysis revealed a mean bias of +10.1° with wide limits of agreement (3.8° to 16.4°). Deming regression yielded the calibration equation Radiographic CPA = (P-APA × 1.371) − 21.883. ROC analysis of calibrated values yielded an AUC of 0.885 (95% CI, 0.820–0.951), with an optimal cutoff of 22.8° (sensitivity, 100%; specificity, 61.1%), corresponding to 32.6° on the uncalibrated photographic scale. Conclusions: Conventional weight-bearing radiography remains the reference standard for diagnosis and clinical decision-making in pes planus. The smartphone-derived photographic arch pitch angle is a non-equivalent surrogate measure that shows substantial systematic bias and limited agreement with radiographic calcaneal pitch, and therefore cannot replace weight-bearing radiographs. Smartphone photogrammetry may be used only as a complementary tool for preliminary screening or telemedicine support; any positive or equivocal findings require radiographic confirmation. Full article

Improving the ride comfort of commercial vehicles is crucial for driver health and operational safety. This study focuses on optimizing the parameters of a cab suspension system to improve its vibration isolation performance. Initially, nonlinear fitting was applied to experimental data characterizing air spring stiffness and damping, which informed the development of a multi-body rigid-flexible coupled dynamic model of the suspension system; its dynamic characteristics were subsequently validated through modal analysis. Road excitation data, filtered through the chassis suspension, were collected during vehicle testing, and displacement excitations for ride comfort simulation were reconstructed using virtual iteration technology. Thereafter, an integrated ISIGHT platform, combining ADAMS and MATLAB, was employed to systematically optimize suspension parameters and key bushing stiffness via a multi-island genetic algorithm. The optimization results demonstrated significant performance improvements: on General roads, the overall weighted root-mean-square acceleration was markedly reduced with enhanced isolation efficiency; on Belgian pave roads, resonance in the cab’s X-axis direction was effectively suppressed; and on Cobblestone roads, the pitch angle was successfully constrained within the design limit. This research provides an effective parameter matching methodology for performance optimization of cab suspension systems. Full article

The depletion of fossil fuel resources and the growing need for sustainable energy solutions have increased interest in vertical axis wind turbines (VAWTs), which offer advantages in urban and variable-wind environments but often exhibit limited performance at low tip speed ratios (TSRs). This study optimizes VAWT aerodynamic behavior across a wide TSR range by varying three geometric parameters: maximum thickness position ($a/b$), relative thickness (m), and pitch angle ($\beta$). A two-dimensional computational fluid dynamics (CFD) framework, combined with the Metamodel of Optimal Prognosis (MOP), was used to build surrogate models, perform sensitivity analyses, and identify optimal profiles through gradient-based optimization of the integrated $C_p$–$\lambda$ curve. The Joukowsky transformation was employed for efficient geometric parameterization while maintaining aerodynamic adaptability. The optimized airfoils consistently outperformed the baseline NACA 0021, yielding up to a 14.4% improvement at $\lambda =2.64$ and an average increase of 10.7% across all evaluated TSRs. Flow-field analysis confirmed reduced separation, smoother pressure gradients, and enhanced torque generation. Overall, the proposed methodology provides a robust and computationally efficient framework for multi-TSR optimization, integrating Joukowsky-based parameterization with surrogate modeling to improve VAWT performance under diverse operating conditions. Full article

The optimization of low-Reynolds-number airfoils for micro unmanned aerial vehicles (UAVs) is challenging due to strong geometric nonlinearities, tight endurance requirements, and the need to maintain performance across multiple operating conditions. Classical surrogate-assisted optimization (SAO) methods combined with genetic algorithms become increasingly expensive and less reliable when class–shape transformation (CST)-based geometries are coupled with several flight conditions. Although deep learning surrogates have higher expressive power, their use in this context is often limited by insufficient local feature extraction, weak adaptation to changes in operating conditions, and a lack of robustness analysis. In this study, we construct a task-specific convolutional neural network–long short-term memory (CNN–LSTM) surrogate that jointly predicts the power factor, lift, and drag coefficients at three representative operating conditions (cruise, forward flight, and maneuver) for the same CST-parameterized airfoil and integrate it into an Non-dominated Sorting Genetic Algorithm II (NSGA-II)-based three-objective optimization framework. The CNN encoder captures local geometric sensitivities, while the LSTM aggregates dependencies across operating conditions, forming a compact encoder–aggregator tailored to low-Re micro-UAV design. Trained on a computational fluid dynamics (CFD) dataset from a validated SD7032-based pipeline, the proposed surrogate achieves substantially lower prediction errors than several fully connected and single-condition baselines and maintains more favorable error distributions on CST-family parameter-range extrapolation samples (±40%, geometry-valid) under the same CFD setup, while being about three orders of magnitude faster than conventional CFD during inference. When embedded in NSGA-II under thickness and pitching-moment constraints, the surrogate enables efficient exploration of the design space and yields an optimized airfoil that simultaneously improves power factor, reduces drag, and increases lift compared with the baseline SD7032. This work therefore contributes a three-condition surrogate–optimizer workflow and physically interpretable low-Re micro-UAV design insights, rather than introducing a new generic learning or optimization algorithm. Full article

This study employed numerical simulations to investigate the aerodynamic characteristics of a flapping wing by solving the governing incompressible Navier–Stokes equations. Using computational fluid dynamics (CFD), the effect of frequency acceleration on the aerodynamic performance of a two-degrees-of-freedom (DoF) flapping wing in hovering was examined. The results indicate that the pitching frequency acceleration significantly influences the aerodynamic force: positive acceleration enhances lift by up to 2.0 times while maintaining propulsion compared to the case under negative acceleration. This mechanism is attributed to the delayed shedding of the leading-edge vortex (LEV) and the shedding of the trailing-edge vortex (TEV). Moreover, aerodynamic forces are also affected by plunge acceleration, with both negative and positive acceleration contributing to performance improvement. An increase in the acceleration coefficient leads to a notable enhancement in the aerodynamic force; however, the improvement becomes marginal when the coefficient n exceeds 0.4. The underlying flow evolution is illustrated and analyzed through pressure and vorticity contours. These findings on the acceleration effect will be applied to optimize the kinematics and design of flapping wing drones. Full article

Efficient mixing in stirred tanks is essential for chemical and biochemical processes. Tubular baffles offer potential energy savings and multifunctionality (e.g., as heat exchangers); however, their interaction with common impeller types is not well understood. This study uses computational fluid dynamics (CFD) simulations to evaluate the hydrodynamic performance of a novel tubular baffle design compared to conventional flat baffles with three impellers: a Rushton turbine (RT), a pitched blade turbine (PBT), and a hydrofoil (HE3). Dimensionless analysis (power number, N_P; and pumping number, N_Q), flow visualization, and vorticity dynamics were employed. The results show that, by attenuating large-scale recirculation, tubular baffles reduce power consumption by 64%, 13%, and 23% for the HE3, PBT, and RT, respectively. However, the HE3 impeller experienced a 30% decrease in pumping capacity, which confined the flow to the lower tank. The PBT showed a 10% increase in N_Q and intensified bottom circulation. The RT uniquely generated distributed, high-intensity turbulence along the baffle height while maintaining its characteristic dual-loop structure. The analysis critiques the local pumping efficiency metric and advocates for a global flow assessment. The HE3 is optimal for efficient bulk blending at low power; the PBT is optimal for strong bottom circulation processes; and the RT is optimal for applications requiring enhanced interfacial processes, where baffles serve a dual function. This work provides a framework for selecting energy-efficient agitation systems by coupling impeller performance with global tank hydrodynamics. Full article

With the rapid development of mobile robotics, wheeled bipedal robots, which combine the terrain adaptability of legged robots with the high mobility of wheeled systems, have attracted increasing research attention. To address the balance control problem during both standing and locomotion while reducing the influence of noise on control performance, this paper proposes a balance control framework based on a Linear Quadratic Regulator integrated with an Extended Kalman Filter (KLQR). Specifically, a baseline LQR controller is designed using the robot’s dynamic model, where the control input is generated in the form of wheel-hub motor torques. To mitigate measurement noise and suppress oscillatory behavior, an Extended Kalman Filter is applied to smooth the LQR torque output, which is then used as the final control command. Filtering experiments demonstrate that, compared with median filtering and other baseline methods, the proposed EKF-based approach significantly reduces high-frequency torque fluctuations. In particular, the peak-to-peak torque variation is reduced by more than 60%, and large-amplitude torque spikes observed in the baseline LQR controller are effectively eliminated, resulting in continuous and smooth torque output. Static balance experiments show that the proposed KLQR algorithm reduces the pitch-angle oscillation amplitude from approximately ±0.03 rad to ±0.01 rad, corresponding to an oscillation reduction of about threefold. The estimated RMS value of the pitch angle is reduced from approximately 0.010 rad to 0.003 rad, indicating improved convergence and steady-state stability. Furthermore, experiments involving constant-speed straight-line locomotion and turning indicate that the KLQR algorithm maintains stable motion with velocity fluctuations limited to within ±0.05 m/s. The lateral displacement deviation during locomotion remains below 0.02 m, and no abrupt acceleration or deceleration is observed throughout the experiments. Overall, the results demonstrate that applying Extended Kalman filtering to smooth the control torque effectively improves the smoothness and stability of LQR-based balance control for wheeled bipedal robots. Full article

Background: Flexible flatfoot is a common pediatric condition. Surgical intervention is indicated for symptomatic cases unresponsive to conservative treatment. This study evaluates the outcomes of two established procedures, Grice extraarticular subtalar arthrodesis and subtalar arthroereisis, in children treated for symptomatic flatfoot. Methods: A retrospective analysis was conducted on 158 patients (286 feet) treated between 2013 and 2024. Among them, 34 underwent Grice arthrodesis and 124 underwent arthroereisis. Demographic and procedural data were collected, including age, sex, neurological impairment (cerebral palsy), laterality, and concurrent Achilles tendon lengthening. Radiographic parameters assessed pre- and postoperatively included Meary’s, Pitch, and Kite’s angles (frontal and sagittal view), uncovering of the talus, and Cyma line. Only patients with both pre- and postoperative measurements were included in paired analysis. Statistical tests included paired t-tests within groups and Welch’s t-tests for between-group comparisons. Results: Grice patients were younger (mean age 9.0 ± 3.1 years) and included all cerebral palsy cases (18/34; 52.9%), while arthroereisis patients were older (10.8 ± 2.6 years) and typically neurologically normal. Achilles tendon lengthening was performed in 100% of Grice and 48% of arthroereisis cases. Both groups showed significant radiographic improvement across all measured parameters (all p < 0.05). Grice arthrodesis produced greater reductions in Meary’s angle (right Δ = −19.8° ± 9.2 vs. −13.1° ± 7.5; p = 0.024), while arthroereisis yielded larger increases in Pitch angle (left Δ = +9.2° ± 7.2 vs. +5.5° ± 6.2; p = 0.055). Other angular improvements (Kite’s, uncovering, and Cyma line) were statistically significant within both groups but not between groups. Conclusions: Symptomatic flat-valgus foot in children remains a relevant public health issue. Treatment should be individualized, while cases secondary to unrecognized or untreated congenital conditions often require surgery to restore normal foot biomechanics. Full article