Machines

17 pages, 10010 KB

Open AccessArticle

Microstructure Characterization and Mechanical Properties of Dissimilar Al/Al-Li Alloy T-Joints Welded by Friction Stir Welding

by Yanjie Han, Duquan Zuo, Tianyu Xu, Guoling Ma, Shilin Feng, Haoran Fu, Zengqiang Cao and Wenya Li

Machines 2025, 13(9), 852; https://doi.org/10.3390/machines13090852 (registering DOI) - 15 Sep 2025

Abstract

This paper investigates the influence of the internal concave surface structure of the stirring tool and welding parameters on the microstructure and mechanical properties of the T-joint. The analysis reveals that compared to the inner concave surface without spirals, T-joints welded by inner [...] Read more.

This paper investigates the influence of the internal concave surface structure of the stirring tool and welding parameters on the microstructure and mechanical properties of the T-joint. The analysis reveals that compared to the inner concave surface without spirals, T-joints welded by inner concave surfaces with spirals exhibit fewer welding defects. Meanwhile, the microscopic results showed that there is a welding juncture zone between the thermomechanical affected zone and the nugget zone, and a large number of θ’, T₁, and η’ phases precipitate in the nugget zone of the joint, which improves its strength and hardness. When welding speed v, rotational speed w and insertion depth h are 60 mm/min, 350 rpm, and 0.21 mm, respectively, the yield strength, the tensile strength, and the elongation of the T-joint reach their maximum values (352 MPa, 408 MPa and 5%), and the tensile strength represents 68.0% and 71.6% of the base materials, respectively. The fracture mechanism of the joint is a mode of ductile fracture. Furthermore, the T-joint exhibits a “W” and “Z” distribution pattern on both sides of the weld centerline B and A, respectively. Full article

(This article belongs to the Section Material Processing Technology)

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16 pages, 7120 KB

Open AccessArticle

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 (registering DOI) - 15 Sep 2025

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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14 pages, 792 KB

Open AccessArticle

Reliability Assessment for Small-Sample Accelerated Life Tests with Normal Distribution

by Jianchao Guo and Huimin Fu

Machines 2025, 13(9), 850; https://doi.org/10.3390/machines13090850 (registering DOI) - 14 Sep 2025

Abstract

A significant challenge in the accelerated life test (ALT) is the reliance on large sample sizes and multiple stress levels, which results in high costs and long test durations. To address this issue, this paper develops a new reliability assessment method for small-sample [...] Read more.

A significant challenge in the accelerated life test (ALT) is the reliance on large sample sizes and multiple stress levels, which results in high costs and long test durations. To address this issue, this paper develops a new reliability assessment method for small-sample ALTs with normal distribution (or lognormal distribution) and censoring. This method enables a high-confidence evaluation of the percentile lifetime (reliable lifetime) under normal operating stress level using censored data from only two accelerated stress levels. Firstly, a relationship is established between the percentile lifetime at normal stress level and the distribution parameters at accelerated stress levels. Subsequently, an initial estimate of the percentile lifetime is obtained from failure data, and its confidence is then refined using a Bayesian update with the nonfailures. Finally, an exact one-sided lower confidence limit (LCL) for the percentile lifetime and reliability is determined. This paper derives an analytical formula for LCLs under Type-II censoring scenarios and further extend the method to accommodate Type-I censored and general incomplete data. The Monte Carlo simulations and case studies show that, the proposed methods significantly reduce the required sample size and testing duration while offering superior theoretical rigor and accuracy than the conventional methods. Full article

(This article belongs to the Section Machines Testing and Maintenance)

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22 pages, 1370 KB

Open AccessArticle

Manufacturing Productivity Improvement by Integrating Digital Tools Illustrated in the Optimization of a Hub Assembly Line

by Florina Chiscop, Adrian Ionut Vlase, Carmen-Cristiana Cazacu, Cicerone Laurentiu Popa and Costel Emil Cotet

Machines 2025, 13(9), 849; https://doi.org/10.3390/machines13090849 - 13 Sep 2025

Abstract

Within the context of Industry 4.0, industrial systems are increasingly integrating digital tools such as discrete-event simulation (DES) and digital twins to enhance operational performance and facilitate data-driven decision-making. This research focuses on the design and implementation of an innovative digital twin to [...] Read more.

Within the context of Industry 4.0, industrial systems are increasingly integrating digital tools such as discrete-event simulation (DES) and digital twins to enhance operational performance and facilitate data-driven decision-making. This research focuses on the design and implementation of an innovative digital twin to diagnose and optimize the productivity of manufacturing systems. A key advancement of this tool involves the integration of a material flow simulator, specifically WITNESS Horizon, with a suite of mathematical and digital models to create an integrated manufacturing digital tool. Rather than modeling individual pieces of equipment or isolated workstations, this digital twining approach encompasses the entire manufacturing architecture. To demonstrate the capabilities and efficacy of this integrated tool, we applied it to a real-world case study: the “Hub R2-11” production line. Utilizing the diagnostic features of the tool for this case study, we identified significant bottlenecks, revealing that over 70% of the conveyor was blocked and more than 60% of the workstation was underutilized. Utilizing the simulation and optimization features of the tool, we increased productivity by restructuring the manufacturing architecture. This involved implementing parallel machining, regulating inputs, and incorporating robotic palletizing. The resultant manufacturing architecture demonstrated a substantial improvement, increasing weekly pallet output from 17 to 41 while reducing conveyor block time by more than 50%. Additionally, a financial assessment indicated a favorable Net Present Value (NPV) and an Internal Rate of Return (IRR) exceeding 35% over three years. The research presented here employs a digital approach grounded in realistic operational constraints, effectively bridging technical innovations with economic feasibility. The findings underscore that this integrated manufacturing digital tool presents a scientifically robust and economically sound strategy for optimizing production systems. Full article

(This article belongs to the Section Robotics, Mechatronics and Intelligent Machines)

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24 pages, 6036 KB

Open AccessArticle

Modeling and Parameter Balancing of Launch Vehicle Guidance System Integrated System Engineering Method

by Wenfeng Zhang, Ke Yue, Shan Luo, Yili Jin, Hangyu Li and Zhilin Jin

Machines 2025, 13(9), 848; https://doi.org/10.3390/machines13090848 - 12 Sep 2025

Abstract

The increasing number of space exploration missions and the complexity of exploration missions have brought great challenges to the design of launch vehicles. The guidance system is the key subsystem of launch vehicles and the key to the success of launch. Traditional document-based [...] Read more.

The increasing number of space exploration missions and the complexity of exploration missions have brought great challenges to the design of launch vehicles. The guidance system is the key subsystem of launch vehicles and the key to the success of launch. Traditional document-based design patterns have been increasingly unable to cope with the problems of insufficient expression, rapid change analysis, and design iteration brought by the increase in system complexity. Employing the MBSE (Model-Based Systems Engineering) method in guidance system design has the advantages of integrated design, closed-loop verification, and fast iteration. The co-simulation between the system-level MBSE model—which captures requirements, functions, and architecture—and domain model (e.g., CAD models and MATLAB-based guidance algorithms, representing discipline-specific implementation models) is conducive to verification and accurate trade-off analysis under frequent changes in requirements and provides support for the rapid design and selection of the launch vehicle guidance system. Full article

(This article belongs to the Special Issue Advances in AI-Enabled Applications for Robotics and Autonomous Systems)

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22 pages, 5421 KB

Open AccessArticle

Effects of Ultra-High Reynolds Number and Low Mach Number Compressibility on the Static Stall Behavior of a Wind Turbine Airfoil

by Zijian Zhang, Xiufeng Huang, Zijie Zhang, Zeling Zhu, Yingning Qiu, Tongguang Wang and Chengyong Zhu

Machines 2025, 13(9), 847; https://doi.org/10.3390/machines13090847 - 12 Sep 2025

Abstract

The increasing scale of wind turbines introduces significant aerodynamic challenges at ultra-high Reynolds numbers and under conditions of low Mach number compressibility. The stall behavior, flow separation, and boundary layer transition are all significantly changed by these characteristics. However, wind tunnel testing cannot [...] Read more.

The increasing scale of wind turbines introduces significant aerodynamic challenges at ultra-high Reynolds numbers and under conditions of low Mach number compressibility. The stall behavior, flow separation, and boundary layer transition are all significantly changed by these characteristics. However, wind tunnel testing cannot concurrently satisfy Re-Ma similarity, and current design frameworks ignore their associated impacts, leading to a great deal of uncertainty in load prediction and power efficiency for next-generation turbines. To bridge this gap, we utilize high-fidelity CFD simulations combined with parametric scaling to develop a novel size-based decoupling technique. With Re and Ma independently controlled by changing chord length and freestream velocity, the FFA-W3-211 airfoil is used as the benchmark. Static stall prediction accuracy is confirmed by validations against the wind-tunnel experimental data of S809 and VR-7B airfoils. The results show that the influence of a high Reynolds number markedly postpones flow separation and enhances pressure distribution, delaying the onset of stall. In contrast, the effect of a high Mach number hastens flow separation and deteriorates pressure distribution due to shock-induced separation, leading to an earlier occurrence of stall. For angles of attack lower than 12°, the influence of the Reynolds number prevails, effectively counteracting the negative impacts of the Mach number. For angles of attack greater than 12°, the two effects combine to raise the risk of flow instability considerably. This study focuses on independently analyzing the effects of the Reynolds and Mach numbers on the stall behaviors of wind turbine airfoils. Full article

(This article belongs to the Special Issue Aerodynamic Analysis of Wind Turbine Blades)

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16 pages, 1766 KB

Open AccessArticle

Sensorless Speed Controller for the Induction Motor Using State Feedback and Robust Differentiators

by Onofre Morfin, Fernando Ornelas-Tellez, Nahitt Padilla, Maribel Gomez, Oscar Hernandez, Reymundo Ramirez-Betancour and Fredy Valenzuela

Machines 2025, 13(9), 846; https://doi.org/10.3390/machines13090846 - 12 Sep 2025

Abstract

This paper introduces a novel sensorless speed control strategy for squirrel-cage induction motors, which ensures robust operation in the presence of external disturbances by applying the state feedback technique. Based on the induction motor model, the speed controller is synthesized by defining a [...] Read more.

This paper introduces a novel sensorless speed control strategy for squirrel-cage induction motors, which ensures robust operation in the presence of external disturbances by applying the state feedback technique. Based on the induction motor model, the speed controller is synthesized by defining a sliding variable that is driven to zero through the supertwisting control law, ensuring the stabilization of the tracking error. The time derivative of the error variable is estimated using a robust differentiator based on the sliding-mode twisting algorithm, thereby eliminating the need to estimate the load torque. A robust observer is employed to estimate the rotor speed and flux linkages simultaneously. The convergence of the estimated rotor flux linkages is enforced through a discontinuous first-order sliding-mode input, while the convergence of the rotor speed estimate is attained via a quasi-continuous super-twisting sliding-mode input. In the proposed model, the inductance parameters are determined from the magnetizing inductance and the leakage inductances of the stator and rotor. A procedure is also presented for adjusting the stator resistance and leakage inductances, taking into account the squirrel-cage rotor type and the skin effect in alternating current conduction. The performance of the sensorless speed control system under variations in load torque and reference speed is validated through experimental testing. The rotor speed estimation provided by the robust observer is accurate. The reference speed tracking control, evaluated using a 1600–1700 rpm pulse train phase-shifted by 4 s with respect to a 0–0.5 N·m pulse train, demonstrates high precision. Full article

(This article belongs to the Special Issue Sensorless and Adaptive Control of Induction Machines)

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15 pages, 6150 KB

Open AccessArticle

Second-Order Complex-Coefficient Flux Observer with Stator Resistance Estimation for Induction Motor Sensorless Drives

by Kun Zhao, Bao Song, Xiaoqi Tang and Xiangdong Zhou

Machines 2025, 13(9), 845; https://doi.org/10.3390/machines13090845 - 11 Sep 2025

Abstract

The voltage model (VM) is widely used in sensorless induction motor drives owing to its structural simplicity and speed-independence. However, DC offsets in back electromotive force (BEMF) caused by measurement errors can degrade the accuracy of flux and speed estimation. To address this [...] Read more.

The voltage model (VM) is widely used in sensorless induction motor drives owing to its structural simplicity and speed-independence. However, DC offsets in back electromotive force (BEMF) caused by measurement errors can degrade the accuracy of flux and speed estimation. To address this issue, this article proposes a second-order complex-coefficient flux observer (SCFO) that effectively eliminates DC offsets without introducing phase delay and amplitude attenuation, while maintaining excellent dynamic performance. Furthermore, to enhance the robustness of the flux observer against stator resistance variations, an improved stator resistance adaptive law based on the rotating reference frame is proposed. Ultimately, experimental validation on a 1.5 kW induction motor drive platform confirms the effectiveness of the proposed sensorless scheme. Full article

(This article belongs to the Section Electrical Machines and Drives)

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42 pages, 12881 KB

Open AccessReview

A Critical Review of Ultrasonic-Assisted Machining of Titanium Alloys

by Muhammad Fawad Jamil, Qilin Li, Mohammad Keymanesh, Pingfa Feng and Jianfu Zhang

Machines 2025, 13(9), 844; https://doi.org/10.3390/machines13090844 - 11 Sep 2025

Abstract

Ultrasonic-assisted machining (UAM) has emerged as a transformative technology for increasing material removal efficiency, improving surface quality and extending tool life in precision manufacturing. This review specifically focuses on the application of it to titanium aluminide (TiAl) alloys. These alloys are widely used [...] Read more.

Ultrasonic-assisted machining (UAM) has emerged as a transformative technology for increasing material removal efficiency, improving surface quality and extending tool life in precision manufacturing. This review specifically focuses on the application of it to titanium aluminide (TiAl) alloys. These alloys are widely used in aerospace and automotive sectors due to their low density, high strength and poor machinability. This review covers various aspects of UAM, including ultrasonic vibration-assisted turning (UVAT), milling (UVAM) and grinding (UVAG), with emphasis on their influence on the machinability, tool wear behavior and surface integrity. It also highlights the limitations of single-energy field UAM, such as inconsistent energy transmission and tool fatigue, leading to the increasing demand for multi-field techniques. Therefore, the advanced machining strategies, i.e., ultrasonic plasma oxidation-assisted grinding (UPOAG), protective coating-assisted cutting, and dual-field ultrasonic integration (e.g., ultrasonic-magnetic or ultrasonic-laser machining), were discussed in terms of their potential to further improve TiAl alloys processing. In addition, the importance of predictive force models in optimizing UAM processes was also highlighted, emphasizing the role of analytical and AI-driven simulations for better process control. Overall, this review underscores the ongoing evolution of UAM as a cornerstone of high-efficiency and precision manufacturing, while providing a comprehensive outlook on its current applications and future potential in machining TiAl alloys. Full article

(This article belongs to the Special Issue Non-Conventional Machining Technologies for Advanced Materials)

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22 pages, 5267 KB

Open AccessArticle

Rotor-Driven Blade Rotor Volumetric Pump: Enhanced Stability and Flow Uniformity via Kinematic Optimization

by Yuanping He, Feifei Zhao, Bin Lin, Tianyi Sui, Liang Fang and Xingfu Hong

Machines 2025, 13(9), 843; https://doi.org/10.3390/machines13090843 - 11 Sep 2025

Abstract

The Blade Rotor Volumetric Pump (BRVP) integrates the operational advantages of vane pumps and positive displacement pumps, enabling a single unit to efficiently achieve both a high flow rate and a high head. This represents a significant expansion of the existing pump design [...] Read more.

The Blade Rotor Volumetric Pump (BRVP) integrates the operational advantages of vane pumps and positive displacement pumps, enabling a single unit to efficiently achieve both a high flow rate and a high head. This represents a significant expansion of the existing pump design spectrum. However, performance testing of the initial Blade-Driven BRVP (BD-BRVP) prototype revealed critical challenges requiring resolution, including the absence of established design theory and unsatisfactory operational smoothness. This study presents a comprehensive analysis of the BD-BRVP’s design principles, mechanical system, and flow characteristics, grounded in the kinematics of a rotationally symmetric crank-guide rod mechanism. Building on this analysis, we propose an innovative Rotor-Driven BRVP (RD-BRVP) configuration. Our results demonstrate that the RD-BRVP significantly outperforms the BD-BRVP in force transmission efficiency and operational smoothness. Specifically, the RD-BRVP exhibits a 42.5% reduction in rotational speed fluctuation and a 20.75% decrease in flow pulsation rate compared to the BD-BRVP. These performance enhancements are conclusively validated through experimental testing. This research advances the technological maturity of the BRVP concept and establishes a foundation for its future practical deployment. Full article

(This article belongs to the Section Turbomachinery)

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23 pages, 6464 KB

Open AccessArticle

Mechanistic Analysis of Textured IEL and Meshing ASLBC Synergy in Heavy Loads: Characterizing Predefined Micro-Element Configurations

by Jiafu Ruan, Xigui Wang, Yongmei Wang and Weiqiang Zou

Machines 2025, 13(9), 842; https://doi.org/10.3390/machines13090842 - 11 Sep 2025

Abstract

Friction contact regulation has been widely acknowledged, yet research on micro-textured meshing interfaces appears to have reached an impasse. Conventional wisdom holds that the similarity of micro-element configurations is the key factor contributing to textured interface issues. The traditional perception is transcended, and [...] Read more.

Friction contact regulation has been widely acknowledged, yet research on micro-textured meshing interfaces appears to have reached an impasse. Conventional wisdom holds that the similarity of micro-element configurations is the key factor contributing to textured interface issues. The traditional perception is transcended, and a novel method for presetting the optimal parameters of gradientized micro-textured interface elements is proposed. The study has analyzed the Interface Enriched Lubrication (IEL) performance and meshing Anti-Scuffing Load-Bearing Capacity (ASLBC) of periodic symmetrical and continuously gradient micro-elements. By actively regulating IEL behavior through geometric constraint effects, dynamic micro-cavity lubrication storage units are formed, thereby extending the retention time of medium film layers. The textured edges induce micro-vortices, delaying scuffing failures induced by load-bearing. Validation analyses demonstrate that optimal micro-element configurations can distribute contact stress to achieve stress homogenization, with the maximum contact stress reduced by 21%. The localized hydrodynamic effect of micro-textured elements increases interfacial meshing stiffness by 5.32% while decreasing friction torque by 27.3%. This investigation reveals a synergistic mechanism between IEL performance and meshing ASLBC under heavy loads conditions. The findings confirm that gradient-based micro-textured element configuration presetting offers an effective solution to reconcile the inherent trade-off between lubrication and load-bearing performance in heavy loads applications. Full article

(This article belongs to the Section Friction and Tribology)

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32 pages, 38675 KB

Open AccessArticle

Comparative Study and Multi-Objective Optimization of Electromagnetic Performance of Permanent Magnet Vernier Motors with Rotor Auxiliary Teeth

by Yujun Shi, Wenlei Zhao, Qingqing Liu, Jiwei Wang, Yaogang Liu and Haifeng Lu

Machines 2025, 13(9), 841; https://doi.org/10.3390/machines13090841 - 11 Sep 2025

Abstract

Permanent magnet vernier motors (PMVMs) have significant advantages in low-speed direct-drive fields on account of their high torque density, and their performance improvement is still a research hotspot. To enhance the overall electromagnetic performance and provide an alternative solution for low-speed direct-drive applications, [...] Read more.

Permanent magnet vernier motors (PMVMs) have significant advantages in low-speed direct-drive fields on account of their high torque density, and their performance improvement is still a research hotspot. To enhance the overall electromagnetic performance and provide an alternative solution for low-speed direct-drive applications, this paper proposes a permanent magnet vernier motor with rotor auxiliary teeth (denoted as “RAT-PMVM”). Firstly, the structure and working principle of RAT-PMVM are introduced. Then, the two-dimensional (2D) finite element method (FEM) is used to comparatively study the influence of the number, position, and tooth profile of the rotor auxiliary teeth on the electromagnetic performance of the proposed motor. The results show that the RAT-PMVM with trapezoidal teeth (denoted as “TT-PMVM”) achieved improvement in output torque, efficiency, and power factor: the output torque increased from 11.32 Nm to 14.19 Nm, the efficiency increased from 88.5% to 92.2%, and the power factor increased from 0.60 to 0.71. Finally, in order to further reduce the torque ripple and improve the torque, power factor, and efficiency, multi-objective optimization of the TT-PMVM is carried out. The optimization yields a 27.3% increase in torque, a 31.8% reduction in torque ripple ratio, an efficiency improvement from 92.2% to 93%, and a power factor enhancement from 0.73 to 0.81, demonstrating significant potential for low-speed direct-drive applications like industrial robots and wind power generation. Full article

(This article belongs to the Topic Advanced Electrical Machines and Drives Technologies, 2nd Edition)

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3 pages, 176 KB

Open AccessCorrection

Correction: Li et al. Mechanism Design of a Novel Device to Facilitate Mobility, Sit-to-Stand Transfer Movement, and Walking Assistance. Machines 2025, 13, 134

by Bo Li, Xinzhili Chen, Hailiang Liu, Dong Yuan, Jiafeng Zhang and Shiqing Lu

Machines 2025, 13(9), 840; https://doi.org/10.3390/machines13090840 - 11 Sep 2025

Abstract

In the original publication [...] Full article

19 pages, 5202 KB

Open AccessArticle

Orifice Leak Detection in Atmospheric Vertical Cylindrical Storage Tanks Based on SVM

by Gengfeng Zheng, Fuqiang Chen, Xiaohan Liu, Feng Liu and Jinhua Ye

Machines 2025, 13(9), 839; https://doi.org/10.3390/machines13090839 - 10 Sep 2025

Abstract

Leak detection in atmospheric vertical storage tanks is crucial for preventing environmental pollution, ensuring production safety, and reducing economic losses. This study investigates orifice leaks in vertical cylindrical storage tanks under atmospheric pressure using FLUENT 16.0. The simulation reveals a significant abrupt pressure [...] Read more.

Leak detection in atmospheric vertical storage tanks is crucial for preventing environmental pollution, ensuring production safety, and reducing economic losses. This study investigates orifice leaks in vertical cylindrical storage tanks under atmospheric pressure using FLUENT 16.0. The simulation reveals a significant abrupt pressure change at the leak location. Based on the simulation findings, the actual acquired pressure signals during leakage are processed with wavelet threshold denoising, confirming the abrupt pressure change characteristic. Time-domain and waveform features of the denoised signals are extracted to establish a support vector machine (SVM)-based leak detection model. The performance of different kernel functions is compared, with the linear kernel achieving the highest accuracy of 96.55%. Full article

(This article belongs to the Section Machines Testing and Maintenance)

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29 pages, 7047 KB

Open AccessArticle

Performance Optimization of Savonius VAWTs Using Wind Accelerator and Guiding Rotor House for Enhanced Rooftop Urban Energy Harvesting

by Farzad Ghafoorian, Seyed Reza Mirmotahari, Shayan Farajyar, Mehdi Mehrpooya and Mahmood Shafiee

Machines 2025, 13(9), 838; https://doi.org/10.3390/machines13090838 - 10 Sep 2025

Abstract

Savonius drag-based rotors, a type of vertical-axis wind turbine (VAWT), are well-suited for urban environments—particularly residential rooftops—owing to their compact design and ability to capture wind from all directions. However, their relatively low efficiency and narrow operational range pose significant challenges, such as [...] Read more.

Savonius drag-based rotors, a type of vertical-axis wind turbine (VAWT), are well-suited for urban environments—particularly residential rooftops—owing to their compact design and ability to capture wind from all directions. However, their relatively low efficiency and narrow operational range pose significant challenges, such as limited energy output under variable wind conditions and reduced performance across a broad range of tip speed ratios. To address these issues, this study explores flow augmentation using strategically placed deflectors, referred to as Wind Accelerators and Guiding Rotor Houses (WAG-RHs). Four different configurations, including double, triple, oblique, and straight designs, were evaluated against both omni-directional guide vanes (ODGVs) and a conventional rotor. The findings show that the ODGV configuration successfully extends the operational range from a tip speed ratio of 0.5 to 0.6—termed the extended performance point (EPP)—and increases the power coefficient (

C_{p}

) by up to 300% compared to the conventional design. Among all setups, the straight WAG-RH configuration proved most effective, not only achieving the EPP but also delivering a 385% and 264.3% increase in local and AVE

C_{p}

values, respectively compared to the conventional rotor. It also outperformed the ODGV-equipped rotor by 25%, thanks to its radial and dual-plane arrangement. Full article

(This article belongs to the Special Issue Mechanical Design and Aerodynamic Optimization of Wind Turbine Components)

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16 pages, 2638 KB

Open AccessArticle

Global Stiffness Modeling of Robot Drilling System Incorporating End-Effector and Arm Flexibility Based on Virtual Joint Method

by Yao-Feng Zhang, Bao-Guo Yao, Fei Zhang, Xi-Feng Liang, Geng Tao, Yu-Xun Ge and Teng-Fei Niu

Machines 2025, 13(9), 837; https://doi.org/10.3390/machines13090837 - 9 Sep 2025

Abstract

In the new digital era, industrial robots are central to machining and flexible production in intelligent manufacturing. However, the rigidity of the six degrees-of-freedom (DOFs) serial robot is insufficient, which leads to chatter during machining and limits its application in high-precision machining, especially [...] Read more.

In the new digital era, industrial robots are central to machining and flexible production in intelligent manufacturing. However, the rigidity of the six degrees-of-freedom (DOFs) serial robot is insufficient, which leads to chatter during machining and limits its application in high-precision machining, especially in the field of drilling, reaming and milling. A new method was proposed for modeling the global stiffness of the robot drilling system that incorporated the end-effector. Based on the virtual joint method and linear superposition principle, and considering the flexibility of the robot arm, the global stiffness model of the robot drilling system was established by simplifying the modeling process with dual quaternion. The results of the model validation experiments of deformation show that the maximum relative error of resultant end deformation is 8.80%, and the average relative error of resultant end deformation is 7.21%. This method provides a new method of global stiffness modeling for the robot drilling system, including the end-effector, and a new approach for stiffness improvement to overcoming the problem of insufficient robot stiffness in intelligent manufacturing industry. Full article

(This article belongs to the Special Issue The New Digital Era in Industrial Robotics, Mechatronics and Factory Automation)

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14 pages, 2508 KB

Open AccessArticle

Automated Weld Defect Detection in Radiographic Images Using Normalizing Flows

by Morteza Mahvelatishamsabadi and Sudong Lee

Machines 2025, 13(9), 836; https://doi.org/10.3390/machines13090836 - 9 Sep 2025

Abstract

Anomaly detection is a pressing issue, particularly in industrial images. Detecting weld defects in radiographic images is a challenge due to the small signal-to-noise ratio (SNR) and the limited availability of data. In this paper, we propose an automated weld defect detection method [...] Read more.

Anomaly detection is a pressing issue, particularly in industrial images. Detecting weld defects in radiographic images is a challenge due to the small signal-to-noise ratio (SNR) and the limited availability of data. In this paper, we propose an automated weld defect detection method using Normalizing Flows (NFs). We employed various state-of-the-art NF architectures with different feature extractors to detect defects in radiographic images of welds, comprehensively comparing the results with radiographic images of welded steel pipes collected from industrial sites. The results show that the combination of CFlow-AD with a wide residual network-50-2 (WRN-50-2) outperformed the other methods, indicating its effectiveness in anomaly detection. Full article

(This article belongs to the Special Issue Reliability in Mechanical Systems: Innovations and Applications)

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34 pages, 951 KB

Open AccessArticle

The Digital Maturity of Small- and Medium-Sized Enterprises in the Saguenay-Lac-Saint-Jean Region

by Gautier George Yao Quenum, Stéfanie Vallée and Myriam Ertz

Machines 2025, 13(9), 835; https://doi.org/10.3390/machines13090835 - 9 Sep 2025

Abstract

This study examines the digital maturity of small- and medium-sized enterprises (SMEs) in the context of Industry 4.0. Despite growing awareness of the importance of digital transformation, many SMEs encounter structural and strategic challenges that impede their progress. Among their obstacles is the [...] Read more.

This study examines the digital maturity of small- and medium-sized enterprises (SMEs) in the context of Industry 4.0. Despite growing awareness of the importance of digital transformation, many SMEs encounter structural and strategic challenges that impede their progress. Among their obstacles is the inadequacy of digital maturity models used to diagnose digital maturity levels in SMEs due to their typological, sectoral, geographical, and other specific characteristics. Using a constructivist and qualitative approach, we have developed a simplified, inclusive, and holistic assessment framework comprising six key dimensions (technology, culture, organization, people and human resources, strategic planning), associated with six progressive maturity levels. Our findings reveal that most SMEs studied in 2023 exhibit a beginner level of digital maturity. These enterprises are characterized by small-scale digital initiatives, often lacking a clear strategy, with limited or partial digitization of processes and heterogeneous technology adoption. The resulting self-assessment tool provides SMEs with practical guidance to launch, evaluate, and accelerate their digital transformation. This study contributes theoretically by proposing a practical digital maturity model and offering a tool to support SMEs and public policy. It highlights the need for tailored support, strategic alignment, and continuous training to unlock the full potential of Industry 4.0 in less urbanized and resource-constrained areas. Full article

(This article belongs to the Special Issue Smart Manufacturing and Beyond: Bridging Innovation in Industry 4.0 and 5.0)

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25 pages, 10618 KB

Open AccessArticle

Study of the Water Vapor Desublimation Effect on the Camber Morphing Wing Considering Cryogenic Environments

by Yu Zhang, Baobin Hou, Yuchen Li, Yuanjing Wang, Binbin Lv, Guojun Lai and Jingyuan Wang

Machines 2025, 13(9), 834; https://doi.org/10.3390/machines13090834 - 9 Sep 2025

Abstract

The variable camber morphing wing has the potential to achieve improved flight performance across different flight conditions by changing its geometry according to changing flight conditions. Evaluating the subtle aerodynamic benefits of variable camber technology necessitates wind tunnel testing under flight Reynolds number [...] Read more.

The variable camber morphing wing has the potential to achieve improved flight performance across different flight conditions by changing its geometry according to changing flight conditions. Evaluating the subtle aerodynamic benefits of variable camber technology necessitates wind tunnel testing under flight Reynolds number conditions. In high Reynolds number wind tunnels, the cryogenic environment readily damages model surface profiles through desublimation and frost, compromising test data accuracy. Consequently, cryogenic wind tunnels must enforce rigorous water vapor control standards. To address potential water vapor effects during cryogenic wind tunnel testing, high-resolution optical measurement techniques were employed to quantify the spatiotemporal evolution of desublimation frost thickness on a typical supercritical airfoil surface. Combined with numerical simulations, the mechanisms governing the frost layer’s influence on aerodynamic characteristics and flow field structures were systematically investigated. The results reveal that the influence of water vapor desublimation on the aerodynamic characteristics under diverse cryogenic working conditions has a commonality, and the difference in aerodynamic parameters shows an increasing tendency as the frost time increases; water vapor desublimation has an obvious influence on the flow structure of the airfoil and its pressure distribution on the surface, which increases flow instability and leads to the backward shift of the shock wave position; larger frost thickness gradients along the flow direction cause more drastic changes in pressure distribution and flow structure; and a larger rate of water vapor desublimation results from a lower temperature and a higher concentration of water vapor in the test environment, which causes frosting to have a more severe impact on the airfoil’s aerodynamic characteristics and flow structure. The findings establish a technical basis for cryogenic wind tunnel moisture control standards and provide a solid foundation for the refined assessment of aerodynamic benefits of the camber morphing wing. Full article

(This article belongs to the Special Issue Smart Structures and Applications in Aerospace Engineering)

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