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Search Results (319)

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14 pages, 10940 KB  
Article
Living Safely: Low Road Mortality in Squamates near Burgas, Bulgaria
by Nikolay Natchev, Pavlina Marinova, Ivan Telenchev, Nikolay Nedyalkov, Aysun Ali and Teodora Koynova
Ecologies 2025, 6(4), 68; https://doi.org/10.3390/ecologies6040068 - 13 Oct 2025
Viewed by 126
Abstract
The study represents the results of a long-term (2016 to 2021) survey on the herpetofauna inhabiting the vicinity of a heavily loaded section of the road E 87. The investigated road splits a Protected site from the net NATURA 2000 BG0000271 “Mandra-Poda”. The [...] Read more.
The study represents the results of a long-term (2016 to 2021) survey on the herpetofauna inhabiting the vicinity of a heavily loaded section of the road E 87. The investigated road splits a Protected site from the net NATURA 2000 BG0000271 “Mandra-Poda”. The Protected site is known for its high biodiversity and its dense populations of vertebrates, which thrive in the area. Directly near the inspected road and on the pavement, we were able to detect five species of snakes, three species of turtles and two species of lizards. Among the squamates, rare observations were made of the European nose-horned viper (Vipera ammodytes), detected twice, and the European glass lizard (Pseudopus apodus), detected three times. Three other species—the Bloched snake (Elaphe sauromates), the Caspian whipsnake (Dolichophis caspius) and the Rhodos green lizard (Lacerta dyplochondrodes)—were found in larger numbers during some of the field surveys and here we provide information concerning the hot moments of their activity in the vicinity of the road. The Grass snakes (Natrix natrix) and the Dice snakes (N. tessellata) formed dense groups in the direct vicinity (closer than one and half meters) of the investigated road section. Despite the high number of recorded snakes and lizards, only isolated cases of vehicle collisions were observed. We suggest that the local squamate population had developed a complex of ethological specifics related to feeding, basking, shading, and copulation, which helped them to benefit from the road and avoid the risks related to the heavy traffic. Full article
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12 pages, 1169 KB  
Article
Research on Space Object Origin Tracing Approach Using Density Peak Clustering and Distance Feature Optimization
by Jinyan Xue, Yasheng Zhang, Xuefeng Tao and Shuailong Zhao
Appl. Sci. 2025, 15(20), 10943; https://doi.org/10.3390/app152010943 - 11 Oct 2025
Viewed by 184
Abstract
The exponential growth of space objects in near-Earth and geostationary orbits has posed severe threats to space environment safety, with debris clouds from spacecraft breakup events being a critical concern. Debris cloud tracing, as a key technology for locating breakup points, faces dual [...] Read more.
The exponential growth of space objects in near-Earth and geostationary orbits has posed severe threats to space environment safety, with debris clouds from spacecraft breakup events being a critical concern. Debris cloud tracing, as a key technology for locating breakup points, faces dual challenges of insufficient precision in analytical methods and excessive computational load in numerical methods. To balance traceability accuracy with computational efficiency, this paper proposes a breakup time determination method integrating a clustering algorithm and the minimization of average relative distance. The method first calculates the average relative distance between fragment pairs and preliminarily estimates the breakup epoch using a golden section step-size optimization strategy. Subsequently, the density peak clustering (DPC) algorithm is introduced to eliminate abnormal fragments. The breakup epoch is then refined based on the cleansed fragment dataset, achieving high-precision localization. Validation through simulations of real breakup events demonstrates that this method significantly improves localization accuracy. It establishes a highly reliable temporal benchmark for space collision tracing, debris diffusion prediction, and orbital safety management. Full article
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21 pages, 6199 KB  
Article
Structural Responses of the Net System of a Bottom-Mounted Aquaculture Farm in Waves and Currents
by Fuxiang Liu, Haitao Zhu, Guoqing Sun, Yuqin Zhang, Yanyan Wang and Gang Wang
J. Mar. Sci. Eng. 2025, 13(10), 1900; https://doi.org/10.3390/jmse13101900 - 3 Oct 2025
Viewed by 304
Abstract
This study investigates the hydrodynamics of the net system of the bottom-mounted aquaculture farms located in the Bohai Sea, addressing the growing demand for high-quality aquatic products and the limitations of coastal aquaculture. Based on the validation part, the established lumped-mass method integrated [...] Read more.
This study investigates the hydrodynamics of the net system of the bottom-mounted aquaculture farms located in the Bohai Sea, addressing the growing demand for high-quality aquatic products and the limitations of coastal aquaculture. Based on the validation part, the established lumped-mass method integrated with the finite element method ABAQUS/AQUA was employed to evaluate the structural responses of the net system with three arrangement schemes under diverse environmental loads. The hydrodynamic loads on net twines are modeled with Morison formulae. With the motivation of investigating the trade-offs between volume expansions, load distributions, and structural reliabilities, Scheme 1 refers to the baseline design enclosing the basic aquaculture volume, while Scheme 2 targets to increase the aquaculture volume and utilization rate and Scheme 3 seeks to optimize the load distributions instead. The results demonstrate that Scheme 1 provides the optimal balance of structural safety and functional efficiency. Specifically, under survival conditions, Scheme 1 reduces peak bottom tension rope loads by 14% compared to Scheme 2 and limits maximum netting displacement to 4.0 m. It is 21.3% lower than Scheme 3, of which the displacement is 5.08 m. It has been confirmed that Scheme 1 effectively minimizes collision risks, whereas the other schemes exhibit severe collisions. Scheme 1 trades off maximum volume expansion for optimal load management, minimal deformation, and the highest overall structural reliability, making it the recommended design. These findings offer valuable insights for the design and optimization of net systems in offshore aquaculture structures serviced in comparable offshore regions. Full article
(This article belongs to the Special Issue Structural Analysis and Failure Prevention in Offshore Engineering)
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15 pages, 1705 KB  
Article
Enhancing Two-Step Random Access in LEO Satellite Internet an Attack-Aware Adaptive Backoff Indicator (AA-BI)
by Jiajie Dong, Yong Wang, Qingsong Zhao, Ruiqian Ma and Jiaxiong Yang
Future Internet 2025, 17(10), 454; https://doi.org/10.3390/fi17100454 - 1 Oct 2025
Viewed by 235
Abstract
Low-Earth-Orbit Satellite Internet (LEO SI), with its capability for seamless global coverage, is a key solution for connecting IoT devices in areas beyond terrestrial network reach, playing a vital role in building a future ubiquitous IoT system. Inspired by the IEEE 802.15.4 Improved [...] Read more.
Low-Earth-Orbit Satellite Internet (LEO SI), with its capability for seamless global coverage, is a key solution for connecting IoT devices in areas beyond terrestrial network reach, playing a vital role in building a future ubiquitous IoT system. Inspired by the IEEE 802.15.4 Improved Adaptive Backoff Algorithm (I-ABA), this paper proposes an Attack-Aware Adaptive Backoff Indicator (AA-BI) mechanism to enhance the security and robustness of the two-step random access process in LEO SI. The mechanism constructs a composite threat intensity indicator that incorporates collision probability, Denial-of-Service (DoS) attack strength, and replay attack intensity. This quantified threat level is smoothly mapped to a dynamic backoff window to achieve adaptive backoff adjustment. Simulation results demonstrate that, with 200 pieces of user equipment (UE), the AA-BI mechanism significantly improves the access success rate (ASR) and jamming resistance rate (JRR) under various attack scenarios compared to the I-ABA and Binary Exponential Backoff (BEB) algorithms. Notably, under high-attack conditions, AA-BI improves ASR by up to 25.1% and 56.6% over I-ABA and BEB, respectively. Moreover, under high-load conditions with 800 users, AA-BI still maintains superior performance, achieving an ASR of 0.42 and a JRR of 0.68, thereby effectively ensuring the access performance and reliability of satellite Internet in malicious environments. Full article
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20 pages, 3326 KB  
Article
Analysis and Suppression Method of Drag Torque in Wide-Speed No-Load Wet Clutch
by Rui Liu, Chao Wei, Lei Zhang, Lin Zhang, Siwen Liang and Mao Xue
Actuators 2025, 14(10), 466; https://doi.org/10.3390/act14100466 - 25 Sep 2025
Viewed by 319
Abstract
Under no-load conditions, the wet clutch of vehicles generates drag torque across a wide speed range, which increases power loss in the transmission system and significantly impacts its efficiency and reliability. To address the clutch drag issue over a wide speed range, this [...] Read more.
Under no-load conditions, the wet clutch of vehicles generates drag torque across a wide speed range, which increases power loss in the transmission system and significantly impacts its efficiency and reliability. To address the clutch drag issue over a wide speed range, this study first establishes a low-speed drag torque model that simultaneously considers the viscous friction effects in both the complete oil film region and the oil film rupture zone of the friction pair clearance. Subsequently, by solving the fluid-structure interaction dynamics model of the friction plates, the collision force between high-speed friction pairs and the resulting friction torque are determined, forming a method for calculating high-speed collision-induced drag torque. Building on this, a unified drag torque model for wet clutches across a wide speed range is developed, integrating both viscous and collision-induced drag torques. The validity of the wide-speed-range drag torque model is verified through experiments. The results indicate that as oil temperature and friction pair clearance increase, the drag torque decreases and the rotational speed corresponding to the peak drag torque is reduced, while the onset of collision phenomena occurs earlier. Conversely, with an increase in oil supply flow rate, the drag torque rises and the rotational speed corresponding to the peak drag torque increases, but the onset of collision phenomena is delayed. Finally, with the optimization objectives of minimizing the peak drag torque in the low-speed range and the total drag torque at the maximum speed in the high-speed range, an optimization design model for the surface grooves of the clutch friction plates is constructed. An optimized groove pattern is obtained, and its effectiveness in suppressing drag torque across a wide speed range is experimentally validated. Full article
(This article belongs to the Section High Torque/Power Density Actuators)
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16 pages, 7120 KB  
Article
Ultra-Long, Minor-Diameter, Untethered Growing Continuum Robot via Tip Actuation and Steering
by Pan Zhou, Zhaoyi Lin, Lang Zhou, Haili Li, Michael Basin and Jiantao Yao
Machines 2025, 13(9), 851; https://doi.org/10.3390/machines13090851 - 15 Sep 2025
Viewed by 596
Abstract
Continuum robots with outstanding compliance, dexterity, and lean bodies are successfully applied in medicine, aerospace engineering, the nuclear industry, rescue operations, construction, service, and manipulation. However, the inherent low stiffness characteristics of continuum bodies make it challenging to develop ultra-long and small-diameter continuum [...] Read more.
Continuum robots with outstanding compliance, dexterity, and lean bodies are successfully applied in medicine, aerospace engineering, the nuclear industry, rescue operations, construction, service, and manipulation. However, the inherent low stiffness characteristics of continuum bodies make it challenging to develop ultra-long and small-diameter continuum robots. To address this size–scale challenge of continuum robots, we developed an 8 m long continuum robot with a diameter of 23 mm by a tip actuation and growth mechanism. Meanwhile, we also realized the untethered design of the continuum robot, which greatly increased its usable space range, portability, and mobility. Demonstration experiments prove that the developed growing continuum robot has good flexibility and manipulability, as well as the ability to cross obstacles and search for targets. Its continuum body can transport liquids over long distances, providing water, medicine, and other rescue items for trapped individuals. The functionality of an untethered growing continuum robot (UGCR) can be expanded by installing multiple tools, such as a grasping tool at its tip to pick up objects in deep wells, pits, and other scenarios. In addition, we established a static model to predict the deformation of UGCR, and the prediction error of its tip position was within 2.6% of its length. We verified the motion performance of the continuum robot through a series of tests involving workspace, disturbance resistance, collision with obstacles, and load performance, thus proving its good anti-interference ability and collision stability. The main contribution of this work is to provide a technical reference for the development of ultra-long continuum robots based on the tip actuation and steering principle. Full article
(This article belongs to the Special Issue Advances and Challenges in Robotic Manipulation)
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24 pages, 4006 KB  
Article
Online Centralized MPC for Lane Merging in Vehicle Platoons
by Shila Alizadehghobadi, Mukesh Singhal and Reza Ehsani
Sensors 2025, 25(17), 5605; https://doi.org/10.3390/s25175605 - 8 Sep 2025
Viewed by 858
Abstract
In the context of autonomous vehicles, proper lane merging is critical as it can reduce the traffic bottleneck and lead to safer road transportation. To obtain a collision-free and efficient lane merging, advanced control algorithms need to be designed to smoothly coordinate multiple [...] Read more.
In the context of autonomous vehicles, proper lane merging is critical as it can reduce the traffic bottleneck and lead to safer road transportation. To obtain a collision-free and efficient lane merging, advanced control algorithms need to be designed to smoothly coordinate multiple vehicles to form a platoon. Model predictive control (MPC) is such a controller capable of forecasting future states of multiple vehicles by optimizing their control inputs while satisfying the constraints. Prior MPC-based studies mostly utilized offline planning with a precomputed lookup table of feasible maneuvers to model lane merging. Although these model designs reduce the online computational load, they lack flexibility, as they rely on predefined scenarios and cannot easily adapt to dynamic or unpredictable situations. In this study, we present a centralized MPC framework capable of online trajectory tracking under dynamic constraints and disturbances, for collision-free operation in tightly spaced multi-vehicle platoons. To evaluate the flexibility of our online algorithm, we examine the role of prediction horizon—the time window over which future states are forecasted—and platoon size in determining both the feasibility and efficiency of merging maneuvers. Our results reveal that there exists an optimal prediction horizon at which braking and acceleration can be minimized, thereby reducing energy consumption by 35–40%. Additionally, we observe that increasing the prediction horizon beyond the minimum required for feasibility can alter the vehicle sequence in the platoon. Capturing the changes in vehicle sequence (e.g., who leads or yields) when prediction horizon varies, is a consequence of online trajectory optimization. This vehicle sequence change cannot be captured by offline planning that relies on precomputed look-up table maneuvers. We also found that as the number of vehicles increases, the minimum feasible prediction horizon increases significantly. Full article
(This article belongs to the Section Vehicular Sensing)
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28 pages, 15533 KB  
Article
Numerical Study on High-Speed Icebreaking of a Hemispherically Capped Cylinder Based on the Smoothed Particle Hydrodynamics Method
by Xiaowei Cai, Zhenwang Li, Jun Zhang, Jie Zhao and Yanmei Jiao
J. Mar. Sci. Eng. 2025, 13(9), 1637; https://doi.org/10.3390/jmse13091637 - 27 Aug 2025
Viewed by 508
Abstract
This work develops an Updated Lagrangian Smoothed Particle Hydrodynamics (ULSPH) framework to simulate high-speed icebreaking by a hemispherically capped cylinder (HCC). Using a self-programmed C++ code with Drucker–Prager damage criteria, this work systematically analyzes how impact velocity (100–200 m/s), ice thickness (10–40 cm), [...] Read more.
This work develops an Updated Lagrangian Smoothed Particle Hydrodynamics (ULSPH) framework to simulate high-speed icebreaking by a hemispherically capped cylinder (HCC). Using a self-programmed C++ code with Drucker–Prager damage criteria, this work systematically analyzes how impact velocity (100–200 m/s), ice thickness (10–40 cm), and impact angle (60–90°) govern structural loads and ice failure modes. The head of the HCC is always the stress concentration area, and the peak value of the impact force increases non-linearly with increasing the initial velocity from 100 m/s to 200 m/s. The increase in ice layer thickness from 10 cm to 40 cm raises the peak value of the impact force by 18.1%. The ice layer deformation shows three-stage characteristics: collision depression, penetration perforation, and through-spray. When the impact angle α is non-vertical, the strain of the ice layer is asymmetrically distributed, and the component of the peak impact force along the y direction increases significantly with the decrease in the impact angle, reaching 129.3 kN at α = 60°. Results reveal velocity-driven nonlinear force amplification, asymmetric strain distribution at oblique angles, and critical stress concentration at the HCC head, providing design insights for polar equipment. Full article
(This article belongs to the Section Ocean Engineering)
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25 pages, 3845 KB  
Article
Lagrangian Simulation of Sediment Erosion in Francis Turbines Using a Computational Tool in Python Coupled with OpenFOAM
by Mateo Narváez, Jeremy Guamán, Víctor Hugo Hidalgo, Modesto Pérez-Sánchez and Helena M. Ramos
Machines 2025, 13(8), 725; https://doi.org/10.3390/machines13080725 - 15 Aug 2025
Viewed by 538
Abstract
Hydraulic erosion from suspended sediment is a major degradation mechanism in Francis turbines of sediment-laden rivers, especially in Andean hydropower plants. This study presents a Python3.9-based computational tool integrating the empirical Oka erosion model within a Lagrangian particle tracking framework, coupled to single-phase [...] Read more.
Hydraulic erosion from suspended sediment is a major degradation mechanism in Francis turbines of sediment-laden rivers, especially in Andean hydropower plants. This study presents a Python3.9-based computational tool integrating the empirical Oka erosion model within a Lagrangian particle tracking framework, coupled to single-phase CFD in OpenFOAM 10. The novelty lies in a reduced-domain approach that omits the spiral casing and replicates its particle-induced swirl via a custom algorithm, lowering meshing complexity and computational cost while preserving erosion prediction accuracy. The method was applied to a full-scale Francis turbine at the San Francisco hydropower plant in Ecuador (nominal discharge 62.4 m3/s, rated output 115 MW, rotational speed 34.27 rad/s), operating under volcanic and erosive sediment loads. Maximum erosion rates reached ~1.2 × 10−4 mm3/kg, concentrated on runner blade trailing edges and guide vane pressure sides. Impact kinematics showed most collisions at near-normal angles (85°–98°, peak at 92°) and 6–9 m/s velocities, with rare 40 m/s impacts causing over 50× more loss than average. The workflow identifies critical wear zones, supports redesign and coating strategies, and offers a transferable, open-source framework for erosion assessment in turbines under diverse sediment-laden conditions. Full article
(This article belongs to the Special Issue Sustainable Manufacturing and Green Processing Methods, 2nd Edition)
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32 pages, 10173 KB  
Article
Field-Calibrated Nonlinear Finite Element Diagnosis of Localized Stern Damage from Tugboat Collision: A Measurement-Driven Forensic Approach
by Myung-Su Yi and Joo-Shin Park
J. Mar. Sci. Eng. 2025, 13(8), 1523; https://doi.org/10.3390/jmse13081523 - 8 Aug 2025
Viewed by 523
Abstract
This study conducts a high-resolution forensic evaluation of stern structural damage resulting from a tugboat collision during berthing, integrating real-world measurement data with calibrated nonlinear finite element analysis. Based on field-acquired deformation geometry and residual dent profiles at Frame 76, five distinct collision [...] Read more.
This study conducts a high-resolution forensic evaluation of stern structural damage resulting from a tugboat collision during berthing, integrating real-world measurement data with calibrated nonlinear finite element analysis. Based on field-acquired deformation geometry and residual dent profiles at Frame 76, five distinct collision scenarios varying in impact orientation, contact area, and load path were simulated using shell-based nonlinear plastic analysis. Particular attention is given to comparing the plastic equivalent strain (PEEQ), von-Mises stress fields, and residual deformation contours at Point A—the critical zone identified from damage surveys. Among the five cases, Case-2, defined by a vertically eccentric external impact, demonstrated the highest plastic strain intensity (PEEQ > 2.0%), the sharpest post-yield drops in stiffness, and the closest match to the residual dent profile observed in the actual structure. The integrated correlation between field damage and some of the results (strain, stress, and deformed shape) enabled clear identification of the most probable accident mechanism with engineering accuracy. This study proposes a validated, measurement-calibrated nonlinear finite element analysis framework to diagnose stern damage from tugboat collisions, enhancing repair decision-making and structural safety assessment. Such a calibrated forensic strategy enhances the reliability of structural safety predictions in marine collision incidents and supports eco-friendly rescue engineering by minimizing unnecessary structural renewal through precise damage localization. The proposed approach establishes a new benchmark for scenario-driven collision assessment, particularly relevant to sustainable, automation-compatible, and damage-tolerant ship design practices. Full article
(This article belongs to the Special Issue Advanced Studies in Marine Mechanical and Naval Engineering)
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19 pages, 1370 KB  
Article
Airborne-Platform-Assisted Transmission and Control Separation for Multiple Access in Integrated Satellite–Terrestrial Networks
by Chaoran Huang, Xiao Ma, Xiangren Xin, Weijia Han and Yanjie Dong
Sensors 2025, 25(15), 4732; https://doi.org/10.3390/s25154732 - 31 Jul 2025
Viewed by 527
Abstract
Currently, the primary random access protocol for satellite communications is Irregular Repetition Slotted ALOHA (IRSA). This protocol leverages interference cancellation and burst repetition based on probabilistic distributions, achieving up to 80% channel utilization in practical use. However, it faces three significant issues: (1) [...] Read more.
Currently, the primary random access protocol for satellite communications is Irregular Repetition Slotted ALOHA (IRSA). This protocol leverages interference cancellation and burst repetition based on probabilistic distributions, achieving up to 80% channel utilization in practical use. However, it faces three significant issues: (1) low channel utilization with smaller frame sizes; (2) drastic performance degradation under heavy load, where channel utilization can be lower than that of traditional Slotted ALOHA; and (3) even under optimal load and frame sizes, up to 20% of the valuable satellite channel resources are still wasted despite reaching up to 80% channel utilization. In this paper, we propose the Separated Transmission and Control ALOHA (STCA) protocol, which introduces a space–air–ground layered network and separates the access control process from the satellite to an airborne platform, thus preventing collisions in satellite channels. Additionally, the airborne-platform estimates the load to ensure maximum access rates. Simulation results demonstrate that the STCA protocol significantly outperforms the IRSA protocol in terms of channel utilization. Full article
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16 pages, 8118 KB  
Article
The Influence of Long-Term Service on the Mechanical Properties and Energy Dissipation Capacity of Flexible Anti-Collision Rings
by Junhong Zhou, Jia Lu, Wei Jiang, Ang Li, Hancong Shao, Zixiao Huang, Fei Wang and Qiuwei Yang
Coatings 2025, 15(8), 880; https://doi.org/10.3390/coatings15080880 - 27 Jul 2025
Viewed by 466
Abstract
This study investigates the long-term performance of flexible anti-collision rings after 12 years of service on the Xiangshan Port Highway Bridge. Stepwise loading–unloading tests at multiple loading rates (0.8–80 mm/s) were performed on the anti-collision rings, with full-field strain measurement via digital image [...] Read more.
This study investigates the long-term performance of flexible anti-collision rings after 12 years of service on the Xiangshan Port Highway Bridge. Stepwise loading–unloading tests at multiple loading rates (0.8–80 mm/s) were performed on the anti-collision rings, with full-field strain measurement via digital image correlation (DIC) technology. The results show that: The mechanical response of the anti-collision ring shows significant asymmetric tension–compression, with the tensile peak force being 6.8 times that of compression. A modified Johnson–Cook model was developed to accurately characterize the tension–compression force–displacement behavior across varying strain rates (0.001–0.1 s−1). The DIC full-field strain analysis reveals that the clamping fixture significantly influences the tensile deformation mode of the anti-collision ring by constraining its inner wall movement, thereby altering strain distribution patterns. Despite exhibiting a corrosion gradient from severe underwater degradation to minimal surface weathering, all tested rings demonstrated consistent mechanical performance, verifying the robust protective capability of the rubber coating in marine service conditions. Full article
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28 pages, 8337 KB  
Article
Collision Detection Algorithms for Autonomous Loading Operations of LHD-Truck Systems in Unstructured Underground Mining Environments
by Mingyu Lei, Pingan Peng, Liguan Wang, Yongchun Liu, Ru Lei, Chaowei Zhang, Yongqing Zhang and Ya Liu
Mathematics 2025, 13(15), 2359; https://doi.org/10.3390/math13152359 - 23 Jul 2025
Viewed by 681
Abstract
This study addresses collision detection in the unmanned loading of ore from load-haul-dump (LHD) machines into mining trucks in underground metal mines. Such environments present challenges like heavy dust, confined spaces, sensor occlusions, and poor lighting. This work identifies two primary collision risks [...] Read more.
This study addresses collision detection in the unmanned loading of ore from load-haul-dump (LHD) machines into mining trucks in underground metal mines. Such environments present challenges like heavy dust, confined spaces, sensor occlusions, and poor lighting. This work identifies two primary collision risks and proposes corresponding detection strategies. First, for collisions between the bucket and tunnel walls, LiDAR is used to collect 3D point cloud data. The point cloud is processed through filtering, downsampling, clustering, and segmentation to isolate the bucket and tunnel wall. A KD-tree algorithm is then used to compute distances to assess collision risk. Second, for collisions between the bucket and the mining truck, a kinematic model of the LHD’s working device is established using the Denavit–Hartenberg (DH) method. Combined with inclination sensor data and geometric parameters, a formula is derived to calculate the pose of the bucket’s tip. Key points from the bucket and truck are then extracted to perform collision detection using the oriented bounding box (OBB) and the separating axis theorem (SAT). Simulation results confirm that the derived pose estimation formula yields a maximum error of 0.0252 m, and both collision detection algorithms demonstrate robust performance. Full article
(This article belongs to the Special Issue Mathematical Modeling and Analysis in Mining Engineering)
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36 pages, 9902 KB  
Article
Digital-Twin-Enabled Process Monitoring for a Robotic Additive Manufacturing Cell Using Wire-Based Laser Metal Deposition
by Alberto José Alvares, Efrain Rodriguez and Brayan Figueroa
Processes 2025, 13(8), 2335; https://doi.org/10.3390/pr13082335 - 23 Jul 2025
Viewed by 916
Abstract
Digital Twins (DTs) are transforming manufacturing by bridging the physical and digital worlds, enabling real-time insights, predictive analytics, and enhanced decision making. In Industry 4.0, DTs facilitate automation and data integration, while Industry 5.0 emphasizes human-centric, resilient, and sustainable production. However, implementing DTs [...] Read more.
Digital Twins (DTs) are transforming manufacturing by bridging the physical and digital worlds, enabling real-time insights, predictive analytics, and enhanced decision making. In Industry 4.0, DTs facilitate automation and data integration, while Industry 5.0 emphasizes human-centric, resilient, and sustainable production. However, implementing DTs in robotic metal additive manufacturing (AM) remains challenging because of the complexity of the wire-based laser metal deposition (LMD) process, the need for real-time monitoring, and the demand for advanced defect detection to ensure high-quality prints. This work proposes a structured DT architecture for a robotic wire-based LMD cell, following a standard framework. Three DT implementations were developed. First, a real-time 3D simulation in RoboDK, integrated with a 2D Node-RED dashboard, enabled motion validation and live process monitoring via MQTT (message queuing telemetry transport) telemetry, minimizing toolpath errors and collisions. Second, an Industrial IoT-based system using KUKA iiQoT (Industrial Internet of Things Quality of Things) facilitated predictive maintenance by analyzing motor loads, joint temperatures, and energy consumption, allowing early anomaly detection and reducing unplanned downtime. Third, the Meltio dashboard provided real-time insights into the laser temperature, wire tension, and deposition accuracy, ensuring adaptive control based on live telemetry. Additionally, a prescriptive analytics layer leveraging historical data in FireStore was integrated to optimize the process performance, enabling data-driven decision making. Full article
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15 pages, 3980 KB  
Article
Four-Dimensional-Printed Woven Metamaterials for Vibration Reduction and Energy Absorption in Aircraft Landing Gear
by Xiong Wang, Changliang Lin, Liang Li, Yang Lu, Xizhe Zhu and Wenjie Wang
Materials 2025, 18(14), 3371; https://doi.org/10.3390/ma18143371 - 18 Jul 2025
Viewed by 654
Abstract
Addressing the urgent need for lightweight and reusable energy-absorbing materials in aviation impact resistance, this study introduces an innovative multi-directional braided metamaterial design enabled by 4D printing technology. This approach overcomes the dual challenges of intricate manufacturing processes and the limited functionality inherent [...] Read more.
Addressing the urgent need for lightweight and reusable energy-absorbing materials in aviation impact resistance, this study introduces an innovative multi-directional braided metamaterial design enabled by 4D printing technology. This approach overcomes the dual challenges of intricate manufacturing processes and the limited functionality inherent to traditional textile preforms. Six distinct braided structural units (types 1–6) were devised based on periodic trigonometric functions (Y = A sin(12πX)), and integrated with shape memory polylactic acid (SMP-PLA), thereby achieving a synergistic combination of topological architecture and adaptive response characteristics. Compression tests reveal that reducing strip density to 50–25% (as in types 1–3) markedly enhances energy absorption performance, achieving a maximum specific energy absorption of 3.3 J/g. Three-point bending tests further demonstrate that the yarn amplitude parameter A is inversely correlated with load-bearing capacity; for instance, the type 1 structure (A = 3) withstands a maximum load stress of 8 MPa, representing a 100% increase compared to the type 2 structure (A = 4.5). A multi-branch viscoelastic constitutive model elucidates the temperature-dependent stress relaxation behavior during the glass–rubber phase transition and clarifies the relaxation time conversion mechanism governed by the Williams–Landel–Ferry (WLF) and Arrhenius equations. Experimental results further confirm the shape memory effect, with the type 3 structure fully recovering its original shape within 3 s under thermal stimulation at 80 °C, thus addressing the non-reusability issue of conventional energy-absorbing structures. This work establishes a new paradigm for the design of impact-resistant aviation components, particularly in the context of anti-collision structures and reusable energy absorption systems for eVTOL aircraft. Future research should further investigate the regulation of multi-stimulus response behaviors and microstructural optimization to advance the engineering application of smart textile metamaterials in aviation protection systems. Full article
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