Search Results (75)

As offshore wind development moves toward deeper waters, floating offshore wind turbines have become essential for carbon-neutral energy systems. This study experimentally investigates the hydrodynamic coefficients of typical column–heave-plate components under forced oscillations, focusing on the influence of pitch-induced inclination. A circular column without a heave plate and a circular column equipped with a hexagonal heave plate were tested under heave and surge motions with varying periods, amplitudes, and static inclination angles. The static inclinations were used to represent the attitude variation of platform components during large-amplitude pitch responses. Added mass and damping coefficients were identified using the least squares method. The results show that for the heave-plate-equipped column, increasing the inclination from 0° to 5° and 10° reduced the nondimensional heave added mass by approximately 4.3% and 5.9%, respectively, and reduced the nondimensional heave damping by approximately 7.1% and 6.8%. The corresponding reductions in surge added mass were approximately 5.3% and 10.5%, whereas the reductions in surge damping reached approximately 8.2% and 16.4%, indicating that the surge damping is most sensitive to static inclination. These variations may be associated with the altered geometric projection and disturbed flow symmetry of the inclined component, which may affect the attached-fluid volume and energy-dissipation process during forced oscillation. Future studies should further verify the corresponding local separation and vortex-formation mechanisms through detailed flow-field measurements, PIV, or CFD. Full article

Transient contact responses in confined guide channels contain sharp events and parameter-dependent phase shifts, which make fixed-output full-history surrogates difficult to train. This study develops a time-conditioned residual surrogate (TC-ResNet) to propagate uncertainty in the bounded center-of-mass eccentricity components into the transient acceleration responses of a generic pressure-driven, high-overload axisymmetric body. The nonlinear reference model includes prescribed base pressure, wall contact and impact, velocity-dependent friction, gravity, pitch and yaw, and eccentricity. TC-ResNet predicts one response value for each parameter–time query by combining normalized physical parameters with Fourier-embedded time. The axial acceleration is modeled directly, whereas low-frequency radial trends and sliding root-mean-square (RMS) curves represent dominant lateral motion and local vibration intensity. On a common 108-case test set, TC-ResNet achieved the highest coefficient of determination (R²) for a_x^low (0.850), a_x^rms (0.839), and a_z^low (0.801), as well as the highest macro-mean R² (0.848). The fixed-output multilayer perceptron (MLP) remained best for a_y (0.995) and a_z^rms (0.775), demonstrating that the proposed model is not uniformly superior. Interval analysis shows that the prescribed pressure load limits axial sensitivity, whereas radial offsets alter eccentric pressure moments and wall contact; the axial offset primarily changes contact and friction moment arms, and inclination mainly affects the later radial response through gravity decomposition and accumulated contact differences. Accuracy approaches a plateau between 378 and 504 training cases. On the same central processing unit (CPU), TC-ResNet requires 0.081 s per curve (approximately 170× faster than the reference solver), and graphics processing unit (GPU) inference requires 0.019 s per curve. The reported envelopes support qualitative sensitivity analysis, but experimental calibration and validation remain necessary. Full article

Dedicated platforms for floating vertical-axis wind turbines (VAWTs) require an in-depth understanding of their strongly unsteady coupled dynamics, yet the effects of platform configuration on motion stability, aerodynamic loading, and wake recovery remain insufficiently clarified. This study develops a high-fidelity aero-hydro-mooring coupled framework base on computational fluid dynamics (CFD) to compare Φ-type floating VAWTs supported by semi-submersible and spar platforms under identical wind–wave excitation. The results show that the semi-submersible configuration, owing to its larger structural scale near the free surface, experiences stronger wave interaction and more pronounced wave-frequency heave, surge, and pitch responses. The spar configuration reduces wave-frequency hydrodynamic excitation because of its deep-draft slender structure, but it is more prone to mean pitch offset and sway–roll–yaw coupling. Mooring responses are governed by mean surge drift, mean pitch inclination, and wave-frequency motions, with the semi-submersible system exhibiting stronger tension fluctuations and the spar system showing a more uneven load distribution among the mooring lines. Under the examined wind–wave condition, the spar configuration exhibits larger fluctuations in instantaneous power, thrust and single-blade torque than the semi-submersible configuration. Wake analysis indicates that the semi-submersible system maintains stronger wake coherence, while the spar system enhances vortex breakdown, turbulent mixing, and velocity-deficit recovery. These findings support platform selection, load control, and array layout optimization for floating VAWTs. Full article

Surface-breaking cracks in concrete structures can accelerate deterioration by facilitating the ingress of moisture, chlorides, and other aggressive agents. Reliable characterization of crack depth is therefore essential for structural health monitoring and maintenance of concrete infrastructure. This study presents an ultrasonic common midpoint (CMP)-based approach for crack-tip localization and crack-depth characterization in concrete. Ultrasonic measurements were acquired using a pitch-catch configuration in which the transmitter and receiver were positioned symmetrically on both sides of surface crack while maintaining a fixed midpoint. Measurements obtained at multiple transmitter–receiver separations were processed to extract the time-of-arrival (ToA) associated with crack-tip diffraction. The measured ToAs were subsequently used within a travel-time-based localization framework to generate crack-tip images and estimate crack-tip coordinates. The proposed methodology was evaluated on concrete slabs containing vertical and inclined surface-breaking cracks of varying depths. In addition, the approach was applied to a reinforced concrete beam specimen containing thin cracks caused by flexural loading. The localized crack-tip positions from ultrasonic imaging are in good agreement with the observed crack depths and geometries. The proposed method offers a non-destructive approach for crack-tip localization and crack-depth characterization in concrete and may support condition assessment of concrete infrastructure. Full article

The threaded connections used in drilling machines operate under high axial loads and torques. These elements ensure both the reliable fastening of the drill heads and their centering relative to the other components of the structure. For fastening drill heads, threads with specific profiles are used, such as trapezoidal profiles with asymmetric flanks. A profile tool is typically used for manufacturing such profiles. This, in turn, limits the flexibility of the process and increases costs in small-batch and repair production conditions. This study proposes a methodology for machining a buttress thread, with trapezoid side angles of 5° and 45°, using a standard grooving insert. The profile geometry is described analytically through the height of each pass of the threading cycle and the inclination angles of the trapezoid flanks, and the implementation is carried out using a macro program based on synchronized G92 cycles. The final profile is formed by the superposition of helical surfaces with a constant pitch. The approach enables the realization of non-standard trapezoidal profiles without the need for a specially profiled tool. The proposed model serves as a foundation for subsequent research into the geometric accuracy and strength characteristics of the thread profile obtained by this method. Full article

Vortex-induced vibration (VIV) poses a significant serviceability concern for wide streamlined box girders of long-span suspension bridges. This study investigates the VIV performance and aerodynamic mitigation of a wide streamlined box girder with a width-to-depth ratio (B/D) of approximately 10 through sectional model wind tunnel testing. The original cross-section was found to exhibit pronounced heaving and torsional VIV at positive wind angles of attack, with amplitudes considerably exceeding the prescribed serviceability limits. A systematic experimental investigation was conducted to evaluate the influence of three geometric parameters, i.e., wind fairing inclination angle, inspection rail position, and pedestrian railing porosity and panel arrangement, on VIV performance. Experimental results demonstrate that reducing the wind fairing inclination angle from 65° to 45° is the most effective mitigation measure. An appropriate porosity of the pedestrian railing is shown to substantially improve VIV performance. Furthermore, under equivalent overall porosity, a uniformly distributed alternation of solid and ventilated panels yields markedly superior VIV suppression compared with continuously sealed arrangements. Subsequent flutter and aerostatic wind tunnel tests confirm that the recommended cross-section preserves the favorable flutter stability and aerostatic performance of the original design. Strouhal number analysis reveals that the VIV lock-in is governed by St ≈ 0.12. Notably, the St number obtained from the pitching moment coefficient is nearly twice that obtained from the lift coefficient. Full article

Background and Objectives: In degenerative spine disease, compensatory mechanisms are activated to maintain upright posture, extending beyond the spine to involve the pelvis, lower limbs, and feet. These adaptations may be accompanied by differences in foot alignment, which could be associated with sagittal balance. The aim of this study is to investigate the relationship between foot alignment and spinal posture in patients with degenerative spine disease and evaluate whether foot deformities are associated with sagittal imbalance in degenerative spine disease. Materials and Methods: We retrospectively reviewed 98 patients with degenerative spine disease who underwent preoperative standing EOS imaging between 2017 and 2025 at a single academic spine centre. Meary’s angle, talocalcaneal angle, and calcaneal pitch were measured on lateral EOS images to classify feet as flat, normal, or cavus. Spinopelvic parameters were extracted from EOS and conventional radiographs. Differences in spinal parameters across foot groups were compared using ANOVA, and linear regression evaluated associations between sagittal vertical axis (SVA) and foot angles. Results: Among spinopelvic parameters, only SVA significantly differed between foot groups, with flatfoot patients showing greater forward imbalance (p = 0.035). Regression analysis demonstrated an inverse relationship between SVA and both talocalcaneal angle (p = 0.003) and calcaneal pitch (p = 0.034), suggesting that greater forward trunk inclination was associated with flatter feet. Degenerative scoliosis patients demonstrated a bimodal pattern with more flat and cavus feet (p = 0.006), while herniated disc patients more often exhibited flatfoot (p = 0.031). Conclusions: Foot posture abnormalities, particularly flatfoot, are associated with sagittal spinal imbalance, suggesting foot posture may be associated with global alignment and could reflect distal postural adaptations. Full article

The goaf backfilling with the coal gangue is an effective strategy for mitigating the mining-induced surface subsidence and reducing the solid waste accumulation. However, the conventional backfilling methods often suffer from limited transport efficiency, poor material distribution, and high operational cost. The present paper proposes a novel technique using an inclined spiral propeller to propel the gangue particles into the goaf, aiming to improve both the backfill rate and spatial uniformity. A three-dimensional parametric model of the inclined screw conveyor is developed, and the discrete element method (DEM) is employed to simulate the dynamic transport and placement of the gangue particles. An L9 ($3^3$) orthogonal experimental design is implemented to systematically evaluate the effects of the rotational speed (240, 300, 360 r/min), inclination angle ($30°$, $45°$, $60°$), and screw pitch (180, 240, 300 mm) on the two critical performance indicators, namely, filling mass and spreading coverage area. The range analysis and matrix analysis are performed to determine the primary influencing factors and to identify the optimal parameter combination for the multi-objective performance. The results show that the inclination angle is the dominant factor for the filling mass, with a $60°$ angle yielding the highest throughput (38.60 kg). In contrast, the rotational speed is the dominant factor for the spreading coverage area, where an increase from 240 to 360 r/min nearly triples the covered area. The optimal compromise for the comprehensive backfilling performance is the rotational speed 360 r/min, inclination angle $60°$, and screw pitch 300 mm, which simultaneously achieves the high transport capacity (36.65 kg) and the largest spreading area (2.87 ${\mathrm{m}}^2$). The present study provides a theoretical and methodological foundation for the engineering design of efficient, low-cost goaf backfilling systems. Full article

In order to optimize the sealing structure of the electrolytic cell for hydrogen production by electrolysis of water and enhance its sealing performance, a finite element model of the electrolytic cell sealing was established using software. The influence of different parameters of the sealing rib structure on the sealing performance was studied, and the variation law of gasket compressive stress under different sealing rib slot widths, angles, and spacings was explored. The results show that under the material constants of C10 = 7.0 × 10⁻³ and C01 = 6.05 in the Mooney–Rivlin constitutive model of the gasket, the gasket will deform and embed into the sealing rib groove after compression. At the same time, two parts of stress concentration will occur at the contact area between the gasket and the sealing rib groove, namely tensile stress concentration and compressive stress concentration. This stress concentration is the main source of sealing effect in practical work. After adding the sealing rib groove, the contact area between the sealing rib area and the gasket increases. When maximizing the peak sealing compressive stress serves as the optimization criterion, the optimal pitch settles at 0.4 mm; if the optimization objective shifts to attaining the utmost contact area, the preferable spacing amounts to 1 mm, accompanied by a maximum contact area increment of 34.31 percent. After comprehensive deliberation over sealing stress magnitude, functional sealing area, gas tightness efficiency as well as practical engineering applicability, 0.8 mm is pinpointed in this dissertation as the globally optimal spacing dimension. With a sealing rib pitch of 0.8 mm, a breadth of 1 mm, and an inclined angle of 20 degrees, the gasket yields substantial sealing stress alongside optimized post-assembly sealing contact area, wherein 26.44 percent of the overall gasket area contributes to effective sealing performance. Full article

Autonomous UAV landing on dynamic unmanned surface vessel platforms is affected by deck motion and degraded visual observations, which may lead to unsafe final descent decisions. This paper proposes a fully decentralized reliability-enhanced predictive landing method that combines probabilistic perception, visual quality assessment, and model predictive control. Target posterior probability, perception uncertainty, and task-oriented image quality are fused into an online observation reliability index, which is used to adapt observation noise, constrain phase switching, and penalize unreliable descent opportunities. FFT-based dominant-mode identification and Kalman correction are also used to predict deck roll and pitch for landing-window selection. Simulation results show that the proposed method achieves a 90% small-angle landing success rate and keeps the touchdown attitude angle within 5°. Compared with standard MPC, landings within a 15° deck inclination increase from 24% to 82%, and the 80th-percentile touchdown inclination decreases by 9°. Compared with SHMPC, the average solution time decreases from 913 ms to approximately 104 ms per iteration. These results indicate that the proposed reliability-aware framework can reduce unsafe descent decisions and improve landing robustness while maintaining real-time feasibility under degraded maritime visual conditions. Full article

As a key component of sugarcane harvesting machinery, the spiral sugarcane lifter (SSL) enhances harvesting quality by lifting lodged sugarcane (LSC) into a posture suitable for stalk-base cutting and feeding. To improve the SSL’s lifting performance for LSC, this study developed a rigid–flexible coupling (RFC) simulation model of the sugarcane–SSL interaction and conducted kinematic and force analyses to identify the main shortcomings of the original design. Critical structural and operational parameters affecting lifting performance–including the lifting roller pitch, roller diameter, roller inclination angle, and lifter shoe length—were redesigned using mechanism-based constraints and simulation-assisted evaluation. The optimized SSL exhibited increased lifting speed and stability under low–speed, severe–lodging conditions. Under side-forward lodging (side deflection angle = 30°), the average maximum vertical height of the centroid (VHC) increased by 40.36%, and paired comparisons across three simulated lodging-angle scenarios showed significant improvement. Field tests under severe lodging at 0.55 m/s (≈2 km/h) yielded an average absolute simulation–to–field error of 5.37%. These findings support the effectiveness of the proposed parameter redesign for the tested medium-size harvester, although further validation is required under higher forward speeds, greater biomass throughput, and more variable soil conditions. Full article

Modern requirements for highly critical threads, such as drilling tool-joint threads or trapezoidal threads of heavy machine tools, impose requirements for high accuracy and at the same time wear resistance of thread cutters. Conventional thread cutters available on the global market have a profile that coincides with the thread profile. Their rake angle and the angle of inclination of the cutting edge are typically zero. However, to ensure long tool life and high cutting performance, such tools should have optimal values of the geometric parameters of the cutting part, particularly the rake angle and the inclination angle of the cutting edge. Non-zero values of these angles distort the thread profile, and there are currently no established algorithms for profiling such cutters. This analytical study aims to develop an algorithm that enables the straightforward manufacture of high-performance and at high-precision thread cutters with interpolated straight sides profile flanks for producing trapezoidal, triangular and buttress threads, including those made of difficult-to-machine materials. The obtained analytical expressions accurately describe the cutting edge of such cutters as a hyperbola, functionally dependent on geometric parameters such as pitch, diameter and thread profile angle, as well as on the rake angle and the inclination angle of the cutting edge. To simplify manufacturing, methods of rectilinear approximation of the curvilinear profile are proposed. The validity of such a replacement has been theoretically confirmed, as the maximum deviation of the hyperbolic profile from the linear approximation does not exceed 2 micrometers. The results indicate no significant deviations in the profile angle of the cutters with relatively large rake and inclination angles (γ = 10° and λ = 7°). Deviations from the nominal profile angle of the trapezoidal thread profile angle of 15° do not exceed 0.1°, while for tool-joint threads (30°), they range from 0.01° to 0.09°. However, significant deviations in the profile (up to 0.49°) occur in the case of machining buttress threads with a profile of 7°/45°. Experimental verification on a lathe confirms the theoretical results. Full article

In this study, a novel flying legged robot configuration with enhanced obstacle-crossing capability is introduced. Legged robots, especially RHex robots, already possess high obstacle-crossing capability; however, the obstacle size that can be overcome is directly dependent on the leg length. Although stair climbing–descending, obstacle course and inclined surface algorithms have been studied for the RHex robot, flight capability has not been explored. In this study, this improvement is achieved with minimal impact on the RHex’s design by adding just a thruster as an additional propulsion system to propel the robot into flight. The attitude control is realized using the mass actuation of the robot legs, similar to how animals like lizards and cats utilize their limbs or tails as inertial appendages to stabilize their body pitch during mid-air maneuvers. Instead of direct and complete flight control, the aim was a temporary flight similar to obstacle-clearing flights of chickens. Hence, a nonlinear 2D model is developed to investigate the kinematics and dynamics of the RHex robot. Equations of motion are derived, linearized and used in a state feedback regulator design; the regulator is also expanded for reference tracking. Full article

The squat is a fundamental multi-joint movement widely studied in strength training and biomechanics. While numerous experimental and computational studies have examined squat kinematics and joint loading, the mechanisms governing how squat technique adapts to increasing external load remain insufficiently understood. In particular, inverse-dynamics-based approaches often overlook explicit constraints imposed by limited joint moment capacity. This study presents a computational framework for predicting load-dependent adaptations of squat posture. The human body was represented as a multi-segment rigid-body system, with joints modeled as nonlinear rotational elements with bounded moment capacity. A reference squat trajectory was first generated kinematically, and a constrained optimization procedure was then applied at each motion frame to determine a mechanically admissible posture under increasing barbell load. The results show that higher loads lead to systematic posture adaptations, including increased torso inclination and redistribution of rotational demand from the knee toward the hip joint. For the highest load, peak torso pitch increased from 30° to over 40°, while joint utilization exceeded unity, indicating the onset of yielding. These findings identify joint moment capacity as a key constraint governing squat technique and demonstrate the potential of the proposed framework for predictive biomechanical analysis. Full article

This study addresses the problem of actively stabilizing the longitudinal body inclination of a tracked mobile platform operating over uneven terrain. A novel drive system architecture is proposed that combines conventional track traction electric drives with an inertial body-stabilization drive based on a flywheel mounted on the pitch axis between the chassis and the body module. The main contribution of the proposed approach is the coordinated control of the traction drives and the inertial actuator based on a unified dynamic model of the platform. A quadratic performance criterion is formulated, and a coordinated optimal control law is synthesized to limit body angular oscillations while accounting for actuator energy consumption. Simulation results for motion over step-like and random terrain irregularities, as well as under external moment disturbances, demonstrate a significant reduction in both peak and root-mean-square pitch-angle deviations relative to configurations without an inertial actuator and with local body stabilization. The results obtained confirm the potential and effectiveness of inertial stabilization drives as part of coordinated drive control systems for tracked mobile platforms intended for special-purpose applications, and indicate prospects for their use in advanced terrestrial robotic platforms and future space robotic systems operating in challenging environments. Full article