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Bridges situated in northern climate regions, which face severe environmental conditions and daily fatigue loading, are prone to accelerated deterioration and corrosion of their components. The application of carbon fiber–reinforced polymer (CFRP) sheets bonding to the surface of bridge elements has emerged as an attractive solution for enhancing bridge strength. Past studies and field implementations have effectively showcased the viability of this approach in strengthening bridges. An exceptional opportunity arises with the deconstruction of a bridge in Canada, providing a unique chance to assess and study the condition of reinforced concrete elements strengthened with CFRP. These elements have endured real service conditions, including fatigue loads and exposure to aggressive environmental factors. This paper presents the experimental results of a research program that aimed to investigate the residual fatigue life and capacity of 60-year-old reinforced concrete bridge girders, which were strengthened using CFRP sheets. The study focuses on assessing the performance of these girders under different test conditions, providing valuable insights into their remaining fatigue life and load-carrying capabilities. The two 60-year-old girders have been strengthened with CFRP for the last 10 years of the service life of the bridge. The two full-scale girders were tested under 2 million fatigue load cycles and then tested monotonically until failure at the structural lab of the University of Sherbrooke. The test results revealed that the CFRP-strengthening technique can extend the service life of the bridge element and enhance its shear capacity. The CFRP–concrete interface and CFRP sheets showed excellent bonding behavior, as no damage-debonding failure or tensile rupture occurred until the formation of the diagonal shear crack. [ABSTRACT FROM AUTHOR]

In traditional short-term hydropower scheduling problems, which usually determine the optimal power generation schedules within one week, the off-design zone of a hydraulic turbine is modeled as a forbidden zone due to the significantly increased risk of turbine damage when operating within this zone. However, it is still plausible to occasionally operate within this zone for short durations under real-world circumstances. With the integration of Variable Renewable Energy (VRE) into the power system, hydropower, as a dispatchable energy resource, operates complementarily with VRE to smooth overall power generation and enhance system performance. The rapid and frequent adjustments in output power make it inevitable for the hydraulic turbine to operate in the off-design zone. This paper introduces the operating zones associated with various production costs derived from fatigue analysis of the hydraulic turbine and calculated based on the turbine replacement cost. These costs are incorporated into a short-term hybrid scheduling tool based on Mixed Integer Linear Programming (MILP). Including production costs in the optimization problem shifts the turbine's working point from a high-cost zone to a low-cost zone. The resulting production schedule for a Hydro-Solar hybrid power system considers not only short-term economic factors such as day-ahead market prices and water value but also lifetime hydraulic turbine cost, leading to a more comprehensive calculation of the production plan. This research provides valuable insights into the sustainable operation of hydropower plants, balancing short-term profits with lifetime hydraulic turbine costs. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Xinjiang University (Natural Science Edition) is the property of Xinjiang University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Railway Standard Design is the property of Railway Standard Design Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In corrosive environments, concrete structures, such as roads and tunnel inverts, are adversely affected by the combined effects of corrosion and fatigue loading. Fatigue loading accelerates the transmission of corrosion ions, resulting in a rapid degradation of structural performance. To examine the transmission law of corrosion ions under fatigue load, this study proposed an unsteady transmission model of corrosion ions in concrete. In view of the interaction between composite corrosion ions, a set of sulfate-chloride ion coupling transmission equations was established based on Fick's second law. Subsequently, fatigue load parameters were introduced into the corrosion ion diffusion coefficient function according to the concrete fatigue equation, and a corrosion ion transport model under fatigue load was established. Moreover, the influence of fatigue parameters on ion transport behavior was discussed based on parameter analysis. Results demonstrate that fatigue load can accelerate the transmission of corrosion ions, and the corrosion rate is positively related to loading frequency and stress level. However, when the stress level is less than 0.2, fatigue load has little effect on the transmission rate of corrosion ions. This study establishes a link between fatigue load and corrosion ion transport behavior and provides a method for assessing the durability of concrete in corrosive environments. [ABSTRACT FROM AUTHOR]

Fatigue load modeling is crucial for optimizing and assessing the lifespan of floating wind turbines. This study addresses the complex characteristics of fatigue loads on floating wind turbines under the combined effects of wind and waves. We propose a fatigue load modeling approach based on Vine copula theory and machine learning. Firstly, we establish an optimal joint probability distribution model using Vine copula theory for the four-dimensional random variables (wind speed, wave height, wave period, and wind direction), with model fit assessed using the Akaike Information Criterion (AIC), Bayesian Information Criterion (BIC), and Root Mean Square Error (RMSE). Secondly, representative wind and wave load conditions are determined using Monte Carlo sampling based on the established joint probability distribution model. Thirdly, fatigue load simulations are performed using the high-fidelity simulator OpenFAST to compute Damage Equivalent Load (DEL) values for critical components (blade root and tower base). Finally, utilizing measured wind and wave data from the Lianyungang Ocean Observatory in the East China Sea, simulation tests are conducted. We apply five commonly used machine learning models (Kriging, MLP, SVR, BNN, and RF) to develop DEL models for blade root and tower base. The results indicate that the RF model exhibits the smallest prediction error, not exceeding 3.9%, and demonstrates high accuracy, particularly in predicting flapwise fatigue loads at the blade root, achieving prediction accuracies of up to 99.97%. These findings underscore the effectiveness of our approach in accurately predicting fatigue loads under real-world conditions, which is essential for enhancing the reliability and efficiency of floating wind turbines. [ABSTRACT FROM AUTHOR]

The failure of rock in cold regions due to repeated freeze–thaw (F-T) cycles and periodic load-induced fatigue damage presents a significant challenge. This study investigates the evolution of the multi-scale structure of fractured granite under combined freeze–thaw (F-T) cycles and periodic loading and develops a constitutive damage model. The results indicate that after F-T cycles, network cracks develop around pre-existing cracks, accompanied by block-like spalling. After applying the fatigue load, the nuclear magnetic resonance (NMR) T2 spectrum shifts to the right, significantly increasing the amplitude of the third peak. The freeze–thaw process induces a "liquid–solid" phase transition, weakening the original pore structure of the rocks and leading to meso-damage accumulation. The pores in fractured granite progressively enlarge and interconnect, reducing the rock's load-bearing capacity and fatigue resistance. The combined effects of F-T cycles and periodic loading induce particle movement and alter fracture modes within the rock, subsequently affecting its macro-damage characteristics. The theoretical curves of the constitutive model align with the experimental data. The findings can serve as a theoretical reference for preventing and controlling engineering disasters in fractured rock masses in cold regions. [ABSTRACT FROM AUTHOR]

The main cable bent around the saddle of the suspension bridge is subjected to the wind, the vehicle, the bridge's own weight and the corrosive media. The coupling of the three loads and the environments causes the friction, the corrosion, and the fatigue (tribo-corrosion-fatigue) among the wires inside the main cable. In this paper, a wire bending tribo-corrosion-fatigue test rig was designed and developed. The effect of fatigue load on the bending friction behaviors between the cable wires in ultrapure water and 3.5% NaCl solution was explored. The tribological properties and electrochemical corrosion behaviors under different fatigue loading ranges were investigated. The tribo-corrosion-fatigue interaction between the cable wires was quantitatively characterized, and the mechanism of the interaction was analyzed. The results demonstrate that the increasing fatigue load exacerbates the coupling damage of the cable wires attributed to the enhanced interaction. The findings carry theoretical importance when assessing the main cable's deterioration and the load-bearing safety of a suspension bridge. [ABSTRACT FROM AUTHOR]

Frequency response capability is necessary for wind farms (WFs) in the power system with a high proportion of renewable energy. In frequency control, WFs need to meet the grid’s power demand and avoid obvious additional damage to wind turbines (WTs) due to frequency control. In terms of meeting the grid power demand, the actual power characteristics of WTs need to be accurately described. An improved Gaussian Mixture Model (GMM) is used to model the actual measured output of WTs. The wind farm control center can accordingly issue achievable effective power commands to the WTs in the frequency response. In terms of avoiding the structural fatigue increase of WTs, a two-degree-of-freedom control strategy is designed, which simultaneously controls the generator torque and pitch angle and achieves fatigue suppression through multi-objective model predictive control (MOMPC). The simulation results show that the proposed control system can improve the frequency response capability of the WF and reduce the fatigue load of WTs, which has obvious application prospects.

This paper presents a quantitative investigation of the effect of structural damping ratios of the tower and blade vibration modes of wind turbines on wind-induced fatigue loads at critical blade and tower sections. Fatigue loads are used as a relative measure of fatigue life in wind turbine design applications. By increasing the structural damping ratio of each one of the critical structural modes which highly contribute to the overall vibration response, short-term and lifetime fatigue loads at critical tower and blade sections are calculated considering parked and operating conditions for different mean wind speeds as well as lifetime operational conditions. [ABSTRACT FROM AUTHOR]

Copyright of Bulletin of the Chinese Ceramic Society is the property of Bulletin of the Chinese Ceramic Society Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The failure of rock in cold regions due to repeated freeze–thaw (F-T) cycles and periodic load-induced fatigue damage presents a significant challenge. This study investigates the evolution of the multi-scale structure of fractured granite under combined freeze–thaw (F-T) cycles and periodic loading and develops a constitutive damage model. The results indicate that after F-T cycles, network cracks develop around pre-existing cracks, accompanied by block-like spalling. After applying the fatigue load, the nuclear magnetic resonance (NMR) T2 spectrum shifts to the right, significantly increasing the amplitude of the third peak. The freeze–thaw process induces a “liquid–solid” phase transition, weakening the original pore structure of the rocks and leading to meso-damage accumulation. The pores in fractured granite progressively enlarge and interconnect, reducing the rock’s load-bearing capacity and fatigue resistance. The combined effects of F-T cycles and periodic loading induce particle movement and alter fracture modes within the rock, subsequently affecting its macro-damage characteristics. The theoretical curves of the constitutive model align with the experimental data. The findings can serve as a theoretical reference for preventing and controlling engineering disasters in fractured rock masses in cold regions.

Fatigue load modeling is crucial for optimizing and assessing the lifespan of floating wind turbines. This study addresses the complex characteristics of fatigue loads on floating wind turbines under the combined effects of wind and waves. We propose a fatigue load modeling approach based on Vine copula theory and machine learning. Firstly, we establish an optimal joint probability distribution model using Vine copula theory for the four-dimensional random variables (wind speed, wave height, wave period, and wind direction), with model fit assessed using the Akaike Information Criterion (AIC), Bayesian Information Criterion (BIC), and Root Mean Square Error (RMSE). Secondly, representative wind and wave load conditions are determined using Monte Carlo sampling based on the established joint probability distribution model. Thirdly, fatigue load simulations are performed using the high-fidelity simulator OpenFAST to compute Damage Equivalent Load (DEL) values for critical components (blade root and tower base). Finally, utilizing measured wind and wave data from the Lianyungang Ocean Observatory in the East China Sea, simulation tests are conducted. We apply five commonly used machine learning models (Kriging, MLP, SVR, BNN, and RF) to develop DEL models for blade root and tower base. The results indicate that the RF model exhibits the smallest prediction error, not exceeding 3.9%, and demonstrates high accuracy, particularly in predicting flapwise fatigue loads at the blade root, achieving prediction accuracies of up to 99.97%. These findings underscore the effectiveness of our approach in accurately predicting fatigue loads under real-world conditions, which is essential for enhancing the reliability and efficiency of floating wind turbines.

An asynchronous distributed optimal power control (OPC) scheme is proposed to minimize fatigue load in the wind farms (WFs) in this paper. To better satisfy the grid code, each wind turbine (WT) in the scheme is equipped with an energy storage system (ESS) at the DC link of the WT converter. Based on the WT topology, a WT-ESS control model is established, thus developing an OPC scheme to control the generator torque, pitch angle, and ESS output simultaneously for reducing fatigue load. By formulating the model predicted control (MPC)-based optimal problems, the virtual mechanical power control is proposed to regulate the ESSs output for clarifying the power interactions among WTs and ESSs. In order to achieve more effective control of the above three parameters among multiple WTs-ESSs, an asynchronous distributed alternating direction method of multipliers (AD-ADMM) is developed to simultaneously minimize the variations of thrust force, shaft torque, and flapping moment load of the WTs in a wider range. Considering the impact of communication delays, the proposed AD-ADMM algorithm has the higher time efficiency and system robustness. The convergence of the proposed AD-ADMM algorithm is analyzed, and several cases are used to validate the performance of the OPC scheme.© 2017 Elsevier Inc. All rights reserved.

The coupling effect of fatigue loads and hydrodynamic pressure has a considerable impact on the durability of pavement concrete. For moderating crack development and improving toughness, basalt fibres (BF) are applied in pavement concrete. The main purpose of this study is to evaluate the performance of using BF in inhibiting cracks and enhancing the toughness of concrete under various coupling conditions. The three-point flexure toughness of basalt fibres-reinforced concretes subjected to the coupled effect of fatigue load and hydrodynamic pressure were carried out, and the strain field of concrete during the bending test was recorded by the digital image correlation (DIC) technique. The cracking behaviours (fractal dimension, tortuosity, surface roughness) during coupling actions and bending tests were characterised by 3D laser instrument and X-ray computed tomography. The experimental results showed that stress level played a decisive role in the deterioration degree of pavement, as stress level increased from 0.5 to 0.7, the bending loads corresponding to the turning point of Df decreased. The hydrodynamic pressure accelerated crack propagation of concrete, especially when loading cycles exceeded 100,000. The addition of BF changed the micro-crack development model of concrete and significantly increased the fracture energy of concrete under coupling actions. [ABSTRACT FROM AUTHOR]

The floating platform motion of an offshore wind turbine system can exacerbate output power fluctuations and increase fatigue loads. This paper proposes a new scheme based on a fast second-order sliding mode (SOSM) control and an adaptive super-twisting extended state observer to suppress the platform motion and power fluctuation. Firstly, an affine nonlinear model of the floating wind turbine pitch system is constructed. Then, a fast SOSM pitch control law is adopted to adjust the blade pitch angle, and a new adaptive super-twisting extended state observer is constructed to achieve total disturbance observation. Finally, simulations are conducted under two cases of wind and wave conditions based on FAST (fatigue, aerodynamics, structures, and turbulence) and MATLAB/Simulink. Compared with the traditional proportional integral (PI) control scheme and standard super-twisting control scheme, the platform roll under the proposed scheme is reduced by 13% and 4%, and pitch is reduced by 16% and 3% in Case 1. Correspondingly, the roll is reduced by 9% and 15%, and pitch is reduced by 7% and 1% in Case 2. For the tower top pitch and yaw moment, load reductions of 7% and 3% or more are achievable compared with those under the PI control scheme. It is indicated that the proposed scheme is more effective in suppressing floating platform motion, stabilizing output power of the wind turbine system, and reducing tower loads. [ABSTRACT FROM AUTHOR]

Floating offshore wind farm control via real-time turbine repositioning has a potential in significantly enhancing the wind farm efficiency. Although the wind farm power capture increase by moving platforms with aerodynamic force has been verified in a recent study, the investigation and mitigation of the fatigue damage caused by such aerodynamic force manipulated for turbine repositioning is still necessary. To respond to these needs, this paper presents fatigue load controller design for a semisubmersible floating offshore wind turbine, particularly when the turbine position is controlled by the nacelle yaw angle. At various turbine positions determined by nacelle yaw angles and average wind speeds, the designed controller manipulates three blade pitch angles individually and minimizes the fatigue load at the tower base. As the individual blade pitch controller, the linear quadratic regulator is optimized through surrogate optimization by simulating the turbine disturbed by various turbulent wind and irregular wave profiles, and then by searching for a minimum fatigue from these simulations. Fatigue load analysis with the optimized controller leads to the main contribution of this paper, that is, to demonstrate that turbine repositioning can be achieved while allowing for the inclusion of a fatigue reducing controller. In fact, when operating the FOWT with the position controller and fatigue load controller, the fatigue damage at the tower base is reduced by about 40% for different nacelle yaw angles. This result supports the feasibility of position-controlled wind turbines to optimize the wind farm efficiency, thereby drastically reducing the offshore wind energy cost. [ABSTRACT FROM AUTHOR]

The aim of this study is to establish a valid and efficient inspection method for assessing macroscopic mechanical property degradation of ethylene-propylene-diene-monomer (EPDM) by examining crosslinked density variation of microstructure. Inspection methods of mechanical behavior and crosslinked density are based on static compression and 1 H double quantum nuclear magnetic resonance ( 1 H DQ NMR), respectively. After introducing the hyperelastic constitutive model proposed by Yuhai Xiang and designing different conditions of heat-aging and fatigue load, the significant mechanical parameter variation is observed for the hyperelastic constitutive model. The significant impacted factors include heat-aging time and fatigue load except for heat-aging compression strain. The phenomenon is consistent with 1 H DQ NMR test results. We further analyze relationship between macro and micro properties of EPDM. After importing fitting assumption and limitation of 1 H DQ NMR data to control fitting error, the fractions of dangling and sol chains f and residual dipolar couplings constants D res in 1 H DQ NMR parameters show moderate negative ( R 2 = 0.6227 ) and high positive ( R 2 = 0.7312 ) correlation with G c of constitutive model parameters, respectively. Thus the validity and precision of inspection method is proven to estimate behavior variation of EPDM and hopefully the method can be extended to analyze other rubber-like materials. [ABSTRACT FROM AUTHOR]

Copyright of Electric Power Automation Equipment / Dianli Zidonghua Shebei is the property of Electric Power Automation Equipment Press and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Electric Power Automation Equipment / Dianli Zidonghua Shebei is the property of Electric Power Automation Equipment Press and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Vortex generators (VGs) have been proposed as an alternative to the power loss caused by wind turbine blade surface contamination. However, quantitative data on the effects of VGs on blade fatigue load are limited. In this study, the contamination conditions for blade tip airfoil and changes in power and fatigue load in the presence of VGs were analyzed using computational fluid dynamics and load analyses. The power curve and fatigue load of each condition were generated for a National Renewable Energy Laboratory 5 MW reference wind turbine through aeroelastic analysis. The simulations indicated that applying VGs under contamination improved the power by 1 %–3 %; however, the improvement was insufficient to restore them to the uncontaminated condition (clean); rather, the blade root flapwise damage equivalent load increased by 4 %–7 %. Consequently, regular inspection and maintenance are required to minimize power loss as an alternative to applying VGs to contaminated blades. [ABSTRACT FROM AUTHOR]

Yaw misalignment can make a wake steer, which is an effective method to increase the power of wind farms but it also increases the fatigue load of the turbines. In this paper, the combination of yaw offset and pitch control (CYMP) is studied to analyse the potential mitigation of wake, focusing on the wind velocity and turbulence of the wake distribution, power increment, and fatigue load reduction. The simulation case study shows that the method of CYMP can reduce the fatigue load by 10.29% and increase the total power by 1.7% compared with only wake steering in FAST.Fram. The Collaborative MPC (CoMPC) method based on CYMP is proposed to the real-time wake control in this research, which can increase power by more than 2% and reduce thrust by more than 4% than greedy control under 10 m/s turbulent wind. [ABSTRACT FROM AUTHOR]

In order to increase the economic benefits of offshore wind farms, reducing the wake effect on the power and fatigue load of wind farms is one of the fundamental ways. In this study, the optimal method of combing yaw offset and pitch control (CYOPC) is put forward for wind farm power and fatigue loads below rated wind speed. To quantify potential power increase and fatigue loads decrease, three turbines in China’s Binhai offshore wind farm are investigated using FAST.Farm. The simulation studies are carried out in region 2 of turbine operation and compared with under yaw control only. Results indicate that the CYOPC method has the potential to increase power and reduce fatigue load.

The service environment of concrete in the marine environment is harsh, and demands regarding the durability of marine concrete have increased. Marine concrete in harbor and wharf areas suffers from the combined effect of fatigue load, dry–wet cycles, and Cl− erosion, which can result in spalling of the concrete surface, corrosion of the internal reinforcement, and even concrete damage. This paper reviews recent research results on the durability of concrete and reinforced concrete (RC) under the combined effect of fatigue load, dry–wet cycles, and Cl− erosion. We further assess the variation in Cl− transport properties with fatigue load, the causes behind the reduction in the carrying capacity of RC products under fatigue load, the methods of Cl− erosion on concrete under the pressures imposed by dry–wet cycles, and the damage of the protective layer of concrete due to accelerated Cl− erosion caused by the action of dry–wet cycles. Further studies are needed on the durability of concrete under the action of fatigue load, wet and dry cycles, and Cl− erosion, in addition to the testing of the durability of concrete under the combined effects of the afore-mentioned various factors. [ABSTRACT FROM AUTHOR]

With the wake effect between different wind turbines, a wind farm generally aims to achieve the maximum energy capture by implementing the optimal pitch angle and blade tip speed ratio under different wind speeds. During this process, the balance of fatigue load distribution is easily neglected because it is difficult to be considered, and, thus, a high maintenance cost results. Herein, a novel bi-objective optimal wind farm energy capture (OWFEC) is constructed via simultaneously taking the maximum power output and the balance of fatigue load distribution into account. To rapidly acquire the high-quality Pareto optimal solutions, the decomposition-based multi-classifier-assisted evolutionary algorithm is designed for the presented bi-objective OWFEC. In order to evaluate the effectiveness and performance of the proposed technique, the simulations are carried out with three different scales of wind farms, while five familiar Pareto-based meta-heuristic algorithms are introduced for performance comparison. [ABSTRACT FROM AUTHOR]

This study primarily analyzes the frequency regulation capability and fatigue loads of wind turbines based on over-speed control. Initially, a small-signal model of the wind turbine is established, which describes the output characteristics of the wind turbine under different control modes and wind speeds. Next, the model is used to analyze the wind turbine's frequency regulation capability and to calculate the optimal frequency regulation parameter range based on the phase margin. Finally, a combination of frequency domain and time domain analysis is used to examine the influence of over-speed control on the fatigue loads of low-speed shafts, towers, and blades, which determines the wind speed range suitable for frequency regulation. The Fast (Fatigue, Aerodynamics, Structures, and Turbulence) Code V8 is used to simulate the dynamic characteristics of the wind turbine. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Railway Science & Engineering is the property of Journal of Railway Science & Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Tribo-corrosion-fatigue coupling damage greatly affects the service safety of wire rope. A self-made test rig was employed to investigate the influences of fatigue load characteristics (amplitude, stress ratio, maximum) on bending tribo-corrosion-fatigue damage of wire ropes. The tribological properties and electrochemical corrosion of the wire ropes, and the coupling damage and mechanisms were discussed in detail. Results indicate a lower friction coefficient between wire ropes in artificial seawater. The main wear mechanisms in seawater are adhesive wear, fatigue wear, oxidation wear and corrosion wear as compared to abrasive wear, adhesive wear, oxidation wear and fatigue wear in pure water. Lower stress ratios amplify corrosion and adhesive wear. Fatigue fractures are mainly ductile, with stress ratio being a significant factor. Tribo-corrosion-fatigue coupling exacerbates damage in contact ropes compared to fatigue ropes. Seawater increases fatigue rope damage but reduces contact rope damage. Higher fatigue load amplitude and maximum value, and lower stress ratios, increase friction coefficient, deformation, volume loss, wire breakage, and decrease corrosion resistance. These findings provide essential data for assessing wire rope service life under seawater corrosion conditions and ensuring offshore drilling safety. [Display omitted] • The influence of fatigue load on the bending tribo-corrosion-fatigue between steel wire ropes is investigated. • The stress ratio has the greatest effect on the coupling damage (wear, deformation and wire breakage). • Seawater promotes the damage to the fatigue ropes, but inhibits the damage to contact ropes. • The mechanism of tribo-corrosion-fatigue damage is discussed. [ABSTRACT FROM AUTHOR]

Cyclical impact loads will transform into low-frequency fatigue loads during propagation and will induce creep deformation of far-field rock under long-term disturbance loads. Laboratory tests of specimens under different fatigue shear loads were conducted. The mechanical responses and creep laws of the specimen were analyzed in detail. Based on the experimental results, a new constitutive model was explored. The results reveal that the stress‒strain curves of the specimen show a trend of step-path increasing under stable and fatigue load circularly. With an increase in fatigue load, the shear strength and elastic modulus of the specimens decrease gradually, while the corresponding failure strain increases gradually. The damage index composed of peak time and peak shear stress can reflect the failure of rock under fatigue loading, and the fatigue amplitude has the greatest influence on specimen deterioration. A fatigue stage in the shear creep curve occurs and is caused by the fatigue load. The fatigue creep rate increases gradually as the fatigue parameter increases. A combined nonlinear damage creep model based on the Nishihara model, elastic body, nonlinear creep body, and fatigue damage function (termed the NENF model), describing the creep responses of rock, anchor, accelerated creep, and fatigue load, respectively, was established. Compared with test data, the creep equation of the model has good accuracy in describing the whole shear creep process of specimens under fatigue loading and provides a new framework for the stability of anchoring rock masses. In this study, an experimental study on the mechanical responses of marble under different fatigue loads was conducted using a servo-controlled compression shear test machine equipped with an improved fixture system. The mechanical responses and creep laws of the specimen were analyzed in great detail. Based on the experimental results, a combined Nishihara model, elastic body, nonlinear creep body, and fatigue damage function (NENF) model describing the whole process of shear creep in an anchored joint rock mass (AJRM) under fatigue load was established. Compared with test data, the creep equation of the model has a good accuracy in describing the whole shear creep process of the specimen under the combination of stable load and fatigue load. This study provides the theoretical basis for the understanding of the long-term stability in AJRM. [ABSTRACT FROM AUTHOR]

As tidal current and marine hydro-kinetic energy converters start to be deployed in pre-commercial arrays, it is critical that the design conditions are properly characterised. Turbulence is known to influence fatigue loads and power production, so developers use turbulence models to generate unsteady flows in order to simulate device performance. Most such models construct a synthetic flow field using a combination of measured parameters and theoretical assumptions. The majority in use today are based on atmospheric flow conditions and may have limited applicability in tidal environments. In the present work, we compare key turbulence model assumptions (which are recommended by the tidal turbine standards and are used in design software) to turbulence measurements from two tidal test sites in Scotland and Canada. Here, we show that the two sites have different levels of conformity to theoretical models, with significant variability within nearby locations at the same site. The agreement with spectral models is shown to be depth-dependent. The vertical component spectrum is better represented by the Kaimal model, while the streamwise spectrum is better represented by the von Kármán model. With the exception of one site, the shear profiles follow a power law, although with a different exponent to that commonly assumed. Both sites show significant deviations from the theoretical length scales and isotropy ratios. Such deviations are likely to misrepresent the loads experienced by a device. These results highlight the turbulence characteristics at real deployment sites, which are not well represented by current models, and, hence, which must be determined using field measurements. [ABSTRACT FROM AUTHOR]

Rock masses around fluid injection projects are usually subject to complex stress states, including hydraulic pressure, in situ stresses, and fatigue loads. Thus, a series of hydraulic fracturing experiments were performed on granite to simulate such stress states using the true triaxial dynamic testing system. Computed tomographic (CT) imaging was performed to identify the fatigue effects on hydraulic fractures. The results indicate that the increasing amplitudes of cyclic load applied on the minimum principal stress direction will change fracture initiation pressure and generate nonplanar and narrow fractures. When the disturbance direction was changed to the intermediate principal stress, the higher amplitude corresponds to the lower breakdown pressure and the shorter pressurize duration and leads to wider fractures. With the increasing disturbance frequency, complex fatigue cracks were generated, which might weaken the rock strength. The present experiments can enhance the understanding of the hazard of fatigue loads on hydraulic fracturing. Highlights: Cyclic loading applied along the minimum principal stress changes the breakdown pressure.Cyclic loading applied along the intermediate principal stress promotes hydraulic fracture initiation and growth.Cyclic loading affects the width of hydraulic fractures and produces several fatigue fractures. [ABSTRACT FROM AUTHOR]

A series of freeze–thaw (F–T) cycle and multilevel fatigue loading tests are carried out on sandstone samples to explore rock mass's fracture behavior and energy evolution characteristics under the coupling action of F–T cycles and fatigue loads. First, the energy evolution characteristics of the sample are analyzed by the image integration method, and the law of energy storage and energy dissipation of the sample are further discussed. Subsequently, a coupled damage model is established based on the Lemaitre strain equivalence hypothesis. Finally, based on the b value and AF-RA waveform theory, the sample's crack evolution process and failure mode are analyzed using acoustic emission (AE) technology. The results show that the specimen's elastic energy and total energy density under the coupling action increase step-like with increasing the upper limit stress. The dissipated energy density decreases rapidly and stabilizes after the first cycle of each stage. The energy evolution process of the sample obeys the linear energy storage law and the two-stage energy dissipation law, in which the energy dissipation law is transformed from linear to exponential in the accelerated energy release stage. The coupling damage of the sample increases exponentially with the number of cycles, and the damage growth rate is slow at first and then fast. In addition, the crack propagation process of the specimen exhibits a 3-stage characteristic. As the number of F–T cycles increases, the proportion of shear cracks in the sample increases significantly, the failure mode transitions from X-conjugate failure to shear failure with a single oblique section, and the fatigue-softening effect is enhanced. Highlights: Freeze-thaw sandstone sample is tested under multi-level fatigue loads. The linear energy storage law and two-stage energy dissipation law are proposed. The sample has obvious accelerated energy release before failure. A coupling damage model under F–T cycles and fatigue load is established. Facture behavior of the sample is analyzed by b value and AF-RA waveform theory. [ABSTRACT FROM AUTHOR]

Cyclical impact loads will transform into low-frequency fatigue loads during propagation; furthermore, the long-term disturbance of such loads induces the prestress loss of far-field anchored joint rock masses (AJRMs). Laboratory tests of AJRMs under different fatigue shear loads were conducted. The yield pattern of anchors, failure pattern of rock blocks and failure mechanism of joints were analysed. The prestress loss characteristics of anchors were studied in great detail. Based on the experimental results, a prestress loss constitutive model of anchors was explored. The results revealed that the morphology of the yielded zone of the anchor is z-shaped, while the failure patterns of the anchored rock blocks were mainly body cracking, and the stable rock blocks presented exfoliation of the cement mortar. In addition, microfissure growth and macrocrack nucleation under shear forces and fatigue forces resulted in the formation of macroscopic cracks and joint block spalling. A wavy ascent stage in the prestress loss caused by the fatigue load occurred, and the prestress loss increment and rate increased gradually as the fatigue loads increased. The Nishihara model and an elastic body were coupled to establish a coupled model that considers the influence of fatigue load, and a prestress relaxation equation of anchors was derived. When compared with data measured during a real engineering project, the results of the prestress relaxation equation exhibited good accuracy. Highlights: The influence of the fatigue conditions on the prestress loss characteristics of anchors was analysed. The development and aggregation of cracks that initiate along the dominant direction of the fatigue force leads to the loss of the bearing capacity of the joint. A new constitutive model was developed to describe the rock-anchor coupling under fatigue loading. [ABSTRACT FROM AUTHOR]