Search Results (10)

Polymer composite coatings exhibit excellent mechanical properties, chemical resistance, and self-lubricating characteristics, providing an effective solution to address the failure of transmission components under harsh operating conditions, including high-speed, high-pressure, and oil-deficient environments, which often lead to excessive friction and limited bearing performance. This study fabricated three polyamide-imide (PAI) composite coatings modified with monodisperse surface-modified nano-silica (SiO₂) via direct spraying and compared their physicochemical parameters. The tribological performance of the three coatings was evaluated using ring-block high-speed friction and wear tester under continuous loading conditions. The tests were conducted using diesel engine oil CI4-5W40, supplemented with oil-soluble cerium dioxide (CeO₂) nanoparticles as an energy-efficient and restorative additive, as the lubricating medium. The experimental results demonstrated that the PAI composite coating exhibited a load-bearing capacity exceeding 1000 N (66 MPa). The wear mechanism analysis reveals that CeO₂ nanoparticles embedded in the coating surface form a cobblestone-like protective layer. This unique microstructure compensates for the surface pits generated by PAI matrix transfer and minimizes direct contact between the coating and steel ring. Additionally, the synergistic interaction between short carbon fiber (SCF) and the tribofilm contributes to the exceptional tribological properties of the coating, including coefficients of friction as low as 0.04 and wear rates below 0.41 × 10⁻⁸ mm³/N·m. The experimental findings could provide an experimental and theoretical foundation for the application of coatings under conditions involving finished lubricants. Full article

This article proposes a novel tube foundation intended for use under transmission line poles. The glass fibre reinforcement polymer (GFRP) piles were driven into sand. A steel tube pole, approximately 6 m high, was mounted on the foundation. The analysed foundations were designed as a monopile to be implemented in the construction of low- and medium-voltage overhead transmission lines. Experimental field tests of innovative piles made of the composite material were carried out on a 1:1 scale. The aim of this work was to develop an isotropic material model treating the GFRP composite as homogeneous. This approach does not fully reproduce the anisotropic behaviour of the composite, but it allows for the engineering design of structures made of the composite material. Laboratory tests in the form of a static tensile test on the samples and a tensile test on the rings cut from a hollow section were performed. The results of the experimental tests and FEM models of the GFRP rings and monopile embedded in sand were compared. The ultimate limit state (ULS) and serviceability limit state (SLS) of the analysed pile were assessed as 14.4 and 9.6 kNm, respectively. The developed numerical model, based on FEM, allows for the load-bearing capacity of the monopile made of GFRP to be reliably determined. From an engineering point of view, the developed numerical model of the GFRP material can be used to calculate the pile load-bearing capacity using engineering software that has limited capabilities in defining material models. Full article

The continuous expansion of wireless communication application scenarios demands the active tuning of electromagnetic (EM) metamaterials, which is essential for their flexible adaptation to complex EM environments. However, EM reconfigurable systems based on intricate designs and smart materials often exhibit limited flexibility and incur high manufacturing costs. Inspired by mechanical metastructures capable of switching between multistable configurations under repeated deformation, we propose a planar kirigami frequency selective surface (FSS) that enables mechanical control of its resonant frequency. This FSS is composed of periodically arranged copper square-ring resonators embedded in a kirigami-structured ecoflex substrate. Through simple tensile deformation, the shapes and positions of the square-ring resonators on the kirigami substrate are altered, resulting in changes to the coupling between capacitance and inductance, thereby achieving active tuning. Combining EM finite element simulations and transmittance measurements, we demonstrate that biaxial mechanical stretching allows for continuous adjustment of the FSS resonant frequency and −10 dB bandwidth. Additionally, the FSS exhibits excellent polarization and incident angle stability. Structural parameterization of the square-ring kirigami FSS was conducted to elucidate the deformation–electromagnetic coupling mechanism underlying the active tuning. These insights provide a foundation for guiding the application of square-ring kirigami FSS in various practical engineering domains. Full article

Wind turbine (WT) foundations with an embedded steel ring (ESR) are widely used in onshore WTs due to construction convenience. The research group found that WT foundations with damage were often accompanied by blade issues. To investigate the potential correlation between aerodynamic imbalance and fatigue damage of the WT foundation with an ESR, this study focuses on a 2 MW WT with an ESR. It investigates the influence of an error in pitch angle (PAE) on the WT’s foundation load and stress, utilizing one year of SCADA data to analyze the fatigue damage caused by PAE. The main conclusions are as follows: Firstly, the effect of PAE on the amplitude value of load and stress is significantly greater than on the average value of load and stress. Secondly, when the PAE is within the range of −3° to 3°, the foundation fatigue damage incurred over one year is minimal, but once this limit is exceeded, the foundation fatigue damage increases dramatically. Thirdly, the peak value of fatigue damage to the foundation caused by PAE does not necessarily occur in the main wind direction, but in the direction with the highest probability of the occurrence of high wind speeds, and the larger the PAE, the more significant the trend. Full article

The foundation ring (FR) is a steel component embedded within the concrete of a wind turbine foundation, playing a pivotal role in connecting the wind turbine tower to the foundation structure. In this paper, the FR–foundation connection is equivalent to the exposed foundation and the shallow foundation by analyzing the anchorage characteristics of the foundation ring. Based on the ABAQUS concrete damaged plasticity model, full-scale modeling of the wind turbine foundation is carried out. The influence of embedment depth, ring radius and base flange width of the foundation ring on moment capacity is simulated. Based on the observed stress distributions under ultimate loads, analytical expressions were proposed to estimate the variation law of anchorage load-bearing capacity in the ultimate load state. Compared with the numerical simulation, the average errors under different influencing factors are 8.2%, 9.6% and 10.8%, respectively. The results indicate that the base flange provided the majority of the moment capacity, though the contribution of the sidewall increased to 25–50% that of the base flange in later stages. Full article

Recent advances in embedded antenna and sensor technologies for 5G communications have galvanized a response toward the investigation of their electromagnetic performance for urban contexts and civil engineering applications. This article quantitatively investigates the effects of material loading on an evolved antecedent hexagonal complementary split-ring resonator (CSRR)-loaded antenna design through simulation and experimentation. Optimization of the narrowband antenna system was first performed in a simulation environment to achieve resonance at 3.50 GHz, featuring an impedance bandwidth of 1.57% with maximum return loss and theoretical gain values of 20.0 dB and 1.80 dBi, respectively. As a proof-of-concept, a physical prototype is fabricated on a printed circuit board followed by a simulation-based parametric study involving antenna prototypes embedded into Ordinary Portland Cement pastes with varying weight percentages of iron(III) oxide inclusions. Simulation-derived and experimental results are mutually verified, achieving a systemic downward shift in resonant frequency and corresponding variations in impedance matching induced by changes in loading reactance. Finally, an inversion modeling procedure is employed using perturbation theory to extrapolate the relative permittivity of the dielectric loaded materials. Our proposed analysis contributes to optimizing concrete-embedded 5G antenna sensor designs and establishes a foundational framework for estimating unknown dielectric parameters of cementitious composites. Full article

Improving the security of electronic devices that support innovative critical services (digital administrative services, e-health, e-shopping, and on-line banking) is essential to lay the foundations of a secure digital society. Security schemes based on Physical Unclonable Functions (PUFs) take advantage of intrinsic characteristics of the hardware for the online generation of unique digital identifiers and cryptographic keys that allow to ensure the protection of the devices against counterfeiting and to preserve data privacy. This paper tackles the design of a configurable Ring Oscillator (RO) PUF that encompasses several strategies to provide an efficient solution in terms of area, timing response, and performance. RO-PUF implementation on programmable logic devices is conceived to minimize the use of available resources, while operating speed can be optimized by properly selecting the size of the elements used to obtain the PUF response. The work also describes the interface added to the PUF to facilitate its incorporation as hardware Intellectual Property (IP)-modules into embedded systems. The performance of the RO-PUF is proven with an extensive battery of tests, which are executed to analyze the influence of different test strategies on the PUF quality indexes. The configurability of the proposed RO-PUF allows establishing the most suitable “cost/performance/security-level” trade-off for a certain application. Full article

The embedded-ring wind turbine foundations were widely applied in the early development stage of wind power industries because of its properties such as easy installation and adjustment. However, different damages occurred on some embedded-ring wind turbine foundations in recent years. Based on the common damage phenomena of embedded-ring wind turbine foundations, the structural defects and damage mechanisms of embedded-ring wind turbine foundations are analyzed in a gradual way. Cheese head studs are proposed to be welded on the lateral wall of the steel ring to strengthen the connection between the steel ring and the foundation concrete. The foundation pier is elevated 1 m to increase the embedded depth of the steel ring. The circumferential confining pressure is applied on the lateral side of the foundation pier to lead it into a state of pressure. One simplified method is proposed to calculate the contribution of welding studs in this strengthening method. Taking an embedded-ring wind turbine foundation as an example, the numerical analyses for the original foundation and the reinforced one are carried out to compare the stress and strain distribution changes. Based on the numerical results corresponding to the peak and valley value loads, the fatigue life of the concrete and studs are evaluated according to the relevant design codes. The numerical results show that this strengthening method can coordinate the deformation of the embedded steel ring and the foundation concrete by circumferential prestressing and welding studs. The maximum principal stresses of the foundation pier and the fatigue stress range of the concrete around the bottom of the steel ring have been greatly reduced after strengthening. The gaps between the embedded steel ring and the foundation pier are also obviously decreased because of these strengthening measures. The stress concentration phenomena of the concrete around the T-shaped flange have been remarkably improved. The fatigue life can meet the requirements of relevant design codes after strengthening. Therefore, it can be concluded that the safety performance and service life of the embedded-ring foundation can be guaranteed. Full article

In this paper, an experimental torsion resistance-loading system for wind power extended foundation scale models is taken as the research object, and four 1:3 scale model specimens of the foundation ring are tested. The transmission mechanism of torque load in the extended foundation was analyzed, and the proportion of each part bearing the torque load was calculated. Test results showed that when the torque load was small, the torque load transmitted from the upper part was mainly borne by the sidewall adhesion force, as well as the top radial reinforcement. In contrast, the torque load was gradually borne by the anchor flange of the foundation ring in the case of a large torque load. At the middle and late stages of torque loading, the top radial reinforcement of the foundation shared about 20% of the torque load, while the bottom flange of the foundation ring shared about 80%. The torque load is most sensitive to changes in the size of the bottom flange but not sensitive to those in the embedded depth of the foundation ring or in the strength of the foundation concrete. Full article

An embedded-ring foundation connected to the steel tower above it by inserting the steel ring into the concrete foundation is a traditional and widely used form for wind turbine towers. An insufficiently embedded depth of the steel ring leads to stress concentration on the corner of the concrete above the windward-side T-shaped plate. A damage zone of concrete develops, leading to gaps between the steel ring and the foundation concrete and a decline in the restrain stiffness of the foundation pier, which induces a larger horizontal displacement of the steel tower and a decrease in the natural frequency for the wind turbine system. To improve the fatigue life of the concrete around the steel ring under the precondition of not destroying the original foundation, a strengthening method using a circumferential prestressing technique is proposed in this paper. A series of numerical analyses were carried out to analyze the stress state change in the foundation concrete before and after strengthening. The fatigue life of the concrete above the T-shaped plate was evaluated according to CEB-FIP model code (fib Model Code for Concrete Structures 2010). The results show that the strengthening method can effectively decrease the fatigue stress amplitude and improve the fatigue life of the concrete above the T-shaped plate. Full article