Stiffness Degradation Modeling for Composite Wind Turbine Blades Based on Full-Scale Fatigue Testing

In order to provide more insights into the damage propagation composite wind turbine blades(blade)under cyclic fatigue loading,a stiffness degradation model for blade is proposed based on the full-scale fatigue testing of a blade.A novel non-linear fatigue damage accumulation model is proposed using the damage assessment theories of composite laminates for the first time.Then,a stiffness degradation model is established based on the correlation of fatigue damage and residual stiffness of the composite laminates.Finally,a stiffness degradation model for the blade is presented based on the full-scale fatigue testing.The scientific rationale of the proposed stiffness model of blade is verified by using full-scale fatigue test data of blade with a total length of 52.5 m.The results indicate that the proposed stiffness degradation model of the blade agrees well with the fatigue testing results of this blade.This work provides a basis for evaluating the fatigue damage and lifetime of blade under cyclic fatigue loading.

EXPERIENCE WITH THERMOMECHANICAL FATIGUE UNDER SERVICE-TYPE LOADING

The thermomechanical fatigue behaviour of different high temperature alloys has been investigated and is under investigation respectively. The creep-fatigue behaviour of heat resistant steels was investigated by long-term service-type strain cycling tests simulating thermomechanical fatigue (TMF-) loading conditions at the heated surface of e.g. turbine rotors. Single-stage as well as three-stage cycles leads to similar results at the application of the damage accumulation rule. Life prediction which simulates typical combinations of cold starts, warm starts and hot starts has been established successfully for isothermal service-type loading and will be exceeded for thermomechanical loading. Long-term thermomechanical fatigue testing of Thermal Barrier Coating systems show typical delamination damage. An advanced TMF cruciform testing system enables complex multiaxial loading.

Symptom experience in patients with cancer-related fatigue:A systematic review and meta-synthesis

To understand the real experiences of patients with cancer-related fatigue and to promote quality of life,the researchers used computer searches of PubMed,EMbase,CINAHL,PsycINFO,Web of Science,and China National Knowledge Infrastructure,China Biology Medicine disc,Wanfang Data,China Science and Technology Journal Database for relevant qualitative studies from the inception to November 1,2021.The results showed that a total of 16 papers were included,and 57 outcomes were distilled into 9 categories,which were pooled into four integrated outcomes,such as somatic,psychological and social support and so on.It is concluded that patients with cancer-related fatigue are not only in the midst of multidimensional,unspeakable somatic experiences,and complex psychological experiences,they are also hindered in coping with fatigue symptom and social life.Therefore,healthcare professionals should provide health interventions and psychological support to those patients whenever possible.

Fatigue behavior of basalt-aramid and basalt-carbon hybrid fiber reinforced polymer sheets

In order to study the fatigue failure mode and fatigue life laws of basalt-aramid and basalt-carbon hybrid fiber reinforced polymer （ FRP ） sheets, fatigue experiments are carried out, considering two hybrid ratios of 1 ： 1 and 2：1 under different stress levels from 0.6 to 0.95. The results show that fractures occur first in carbon fibers or aramid fibers for the specimens with hybrid ratio of 1： 1, namely B1A1 and B1C1, while a fracture occurs first in basalt fibers for the specimens with a hybrid ratio of 2： 1, namely B2A1 and B2C1. The fatigue lives of the hybrid FRP sheets increase with the improvement of the content of carbon fibers or aramid fibers, and the influence of the carbon fibers content improvement to fatigue life is more significant. The fatigue performance of B2A1 is relatively worse, while the fatigue performance of B1C1 and B2C1 is relatively better. Finally, a new fatigue stiffness degradation model with dual variables and double inflection points is presented, which is applicable to both hybrid and normal FRP sheets.

PRE-CORROSION FATIGUE NOTCH FACTOR

The notched and smooth specimens of aluminum alloy LC4CS soaked in EXCO solution for different time are tested under the constant amplitude cyclic loading to obtain S-N curves and fatigue notch factors with different pre-corrosion time. By analyzing the corrosion process of LC4CS specimens in EXCO solution, the influ- ence mechanism of corrosion on fatigue notch factor is expounded. Then, a two-parameter model used to describe the change of corrosion fatigue notch factor with time is established and verified by experiment. The results show that the pre-corrosion fatigue notch factor of LC4CS material decreases at first and then increases with the increasing pre-corrosion time. The inflection point appears at the beginning of denudation stage.

An Advanced Control Strategy for Dual-Actuator Driving System in Full-Scale Fatigue Test of Wind Turbine Blades

A new dual-actuator fatigue loading system of wind turbine blades was designed.Compared with the traditional pendulum loading mode,the masses in this system only moved linearly along the loading direction to increase the exciting force.However,the two actuators and the blade constituted a complicated non-linear energy transferring system,which led to the non-synchronization of actuators.On-site test results showed that the virtual spindle synchronous strategy commonly used in synchronous control was undesirable and caused the instability of the blade’s amplitude eventually.A cross-coupled control strategy based on the active disturbance rejection algorithm was proposed.Firstly,a control system model was built according to the synchronization error and tracking error.Furthermore,based on arranging the transition process,estimating the system state and error feedback,and compensating disturbance,an active disturbance rejection controller was designed by adopting the optimal control function.Finally,on-site test results showed that the cross-coupled control strategy based on the active disturbance rejection algorithm could ensure the synchronization of two actuators.The maximum speed synchronization error of the two motors was less than 16 RPM,the displacement synchronization error of the two actuators was less than 0.25 mm and approaching zero after 4 seconds,and the peak value of vibration of the blade was less than 5 mm,which satisfied the fatigue test requirement.

Mechanical behaviour analysis and support system field experiment of confined concrete arches

Soft rock control is a big challenge in underground engineering.As for this problem,a high-strength support technique of confined concrete(CC)arches is proposed and studied in this paper.Based on full-scale mechanical test system of arch,research is made on the failure mechanism and mechanical properties of CC arch.Then,a mechanical calculation model of circular section is established for the arches with arbitrary section and unequal rigidity;a calculation formula is deduced for the internal force of the arch;an analysis is made on the influence of different factors on the internal force of the arch;and a calculation formula is got for the bearing capacity of CC arch through the strength criterion of bearing capacity.With numerical calculation and laboratory experiment,the ultimate bearing capacity and internal force distribution is analyzed for CC arches.The research results show that:1)CC arch is 2.31 times higher in strength than the U-shaped steel arch and has better stability;2)The key damage position of the arch is the two sides;3)Theoretical analysis,numerical calculation and laboratory experiment have good consistency in the internal force distribution,bearing capacity,and deformation and failure modes of the arch.All of that verifies the correctness of the theoretical calculation.Based on the above results,a field experiment is carried out in Liangjia Mine.Compared with the U-shaped steel arch support,CC arch support is more effective in surrounding rock deformation control.The research results can provide a basis for the design of CC arch support in underground engineering.

Experimental and Numerical Study on the Gas Explosion in Urban Regulator Station

Regulator station is an important part in the urban gas transmission and distribution system.Once gas explosion occurs,the real explosion process and consequences of methane gas explosion in the regulator station were not revealed systematically.In this study,a full-scale experiment was carried out to simulate the regulator station explosion process,and some numerical simulations with a commercial CFD software called FLACS were conducted to analyze the effect of ignition and vent conditions on the blast overpressure and flame propagation.The experimental results demonstrated that the peak overpressure increased as the distance from the vent increased within a certain distance.And the maximum overpressure appeared 3 m away from the door,which was about 36.6 kPa.It was found that the pressure-time rising curves obtained from the simulation are basically the same as the ones from the experiment,however,the time of reaching the peak pressure was much shorter.The numerical simulation results show that the peak overpressures show an increase trend as the ignition height decreased and the vent relief pressure increased.It indicates that the damage and peak overpressure of gas explosion could be well predicted by FLACS in different styles of regulator station.In addition,the results help us to understand the internal mechanism and development process of gas explosion better.It also offers technical support for the safety protection of the urban regulator station.

Large scale sand saltation over hard surface:a controlled experiment in still air

Saltation is the major particle movement type in wind erosion process.Saltating sand grains can rebound up to tens of times larger in length and height over hard surface(such as gravel surface)than over loose sand surface.Gravels usually have different faces,causing distinct response of the impacting grains,but the effects of the grain and gravel-surface contact angle on grain rebound are not yet well quantified.We performed full-range controlled experiments of grain saltation using different contact angles,grain sizes and impact speeds in still air,to show that contact angle increases the height of representative saltation path but decreases particle travel length.The results were compared with outputs from the COMprehensive numerical model of SALTation(COMSALT).Large saltation height of 4.8 m and length of 9.0 m were recorded.The maximum and representative saltation height over the gravel surface were found to be about 4.9 times and 12.8 times those over the loose sandy surface,respectively.The maximum saltation length may be reduced by 58%and the representative saltation height may be increased by 77%as contact angle increases from 20°to 40°.We further showed that the collision inertia contributes 60%of the saltation length,and wind contributes to the other 40%.These quantitative findings have important implications for modeling saltation trajectory over gravel surface.

Squat,Stoop,or Semi-squat:A Comparative Experiment on Lifting Technique

There are actually no sufficient data for lifting technique assessment.A laboratory study was undertaken to determine the effect of 3 regular lifting techniques on erector muscle activation,cardiovascular strain and subjective response.Thirty student volunteers participated in the study,and were required to lift a weight with different techniques.Stoop-,squat-,semi-squat-lifting resulted in 3,2 and 1 time of the highest percentage of the maximum voluntary electrical activation(MVE%) respectively.In the same order,the lowest median frequency(MF) existed 1,1 and 2 times.Muscle fatigue was 4 times in squat,36 in semi-squat and 43 in stoop lifting.Heart rate was the highest in squat and lowest in stoop respectively,with a middle level in semi-squat lifting.It may be recommended to adopt mainly the semi-squat technique for daily lifting works.For heavy lifting,it should use the squat technique.Stoop lifting may also be used alternatively but for light things.

Study on Hydrogen Environment Fatigue Test System and Correlative Fatigue Test of Hydrogen Storage Vessel

A 70 MPa hydrogen environment fatigue test system has been designed and applied in the manufacture of a hydrogen storage vessel. The key equipment is a 80 MPa flat steel ribbon wound high pressure hydrogen storage vessel. A reasonable stress distribution has been realized, which is low stress on the liner of the pressure vessel and even stress on the flat ribbon layers. This optimal stress distribution is achieved through the adjustment of the prestress in flat steel ribbons. A control system for the fatigue test system has also been designed. It consists of a double control model, manual control and automatic control, to satisfy different experiment requirements. The system is the only one which can be used in the real hydrogen environmental fatigue test system in China. An experiment for a 70 MPa onboard composite material hydrogen vessel has been carried out on the system. The experimental results from this test are in close agreement with the practical operating conditions.

Experiments on Large-Diameter Welded Hollow Spherical Joint

We experimented on welded hollow spherical joint of a stadium steel roof to investigate the stress and strain distributions on the surface of the joint and determine the ultimate bearing capacity. Then, finite element analysis was made to experimental results. When the test load was 140% of the design load, the stress at the bottom of the fourth wimble pipe reached the yield point. The experimental results agree with the analytical results well.

Experimental Research and Finite Element Analysis on Setting Stiffening Rib of Corner Joints in Gabled Frames

In order to clear constructional design of corner joint, it is necessary to further investi-gate mechanical property of corner joint in gabled frames. Through static test and finite element software analysis of comparing the panel zone with and without inclined stiffener. Some conclusions are given in the article. The load displacement curves show that the capacity of oblique nodes installed within stiffening rib components is enhanced i.e. 40% more than those without stiffening rib nodes. The results reveal that in the gabled frames, the corner node with the inclined stiffening rib can improve the bearing capacity of the specimens. When the extraterritorial flange is tension, the erection of the inclined stiffening rib can prevent structural failure and improve effectually the ductility of the structure.

Influencing factors of fatigue in young and middle-aged patients with coronary heart disease:a cross-sectional study

Objective:To examine the present state of fatigue in young and middle-aged patients with coronary heart disease(CHD)and to identify the elements that may be affecting it.Methods:From December 2020 to June 2021,240 young and middle-aged patients with CHD who were being treated in the cardiology department of a tertiary care hospital in Suzhou were chosen using a convenience sampling method in order to gather data on the patients’sociodemographic status,fatigue,social support,and stress.Results:Of the 240 disseminated questionnaires,220 valid responses were returned,resulting in an effective recovery rate of 91.67%.The frequency of exhaustion was 51.8%,and the fatigue score was(5.27±2.77).The stress score was(11.15±3.36),while the overall social support score was(39.13±4.72).Binary logistic regression analysis indicated that age,exercise,staying up late,stress,social support,high-sensitivity troponin T,high-density lipoprotein,and ejection fraction were independent risk factors for fatigue in young and middle-aged patients with CHD(P<0.05).Conclusions:Fatigue is more prevalent in young and middle-aged patients with CHD.Clinical nurses can create a unique management plan for patients based on their lifestyle and behavioral patterns,stress levels,social support,and clinical signs to reduce fatigue.

Full-scale experiment for segmental linings of deep-buried shield tunnels bearing high inner water pressure:Comparison of mechanical behaviors of continuous-and stagger-jointed structures

Full-scale loading tests were performed on shield segmental linings bearing a high earth pressure and high inner water pressure,focus-ing on the effects of the inner water load and assembly manner on the mechanical properties of the segmental linings.The test results indicate that the deep-buried segmental linings without inner pressure have a high safety reserve.After the action of high inner water pressure,the lining deformation will increase with the reduction of the safety reserve,caused by the significant decrease in the axial force in the linings.Because the bending moment at the segmental joints is transferred to the segment sections in the adjacent ling rings,the convergence deformation,openings of segmental joints,and bolt strains are smaller for the stagger-jointed lining than those for the continuous-jointed lining;however,dislocations appear in the circumferential joints owing to the stagger-jointed assembly.Although it significantly improves the mechanical performance of the segmental lining,stagger-jointed assembly results in compromising the water-proofing safety of circumferential joints.The stagger-jointed assembly manner can be considered to improve the service performance of shield tunnels bearing high inner water pressure on the premise that circumferential joint waterproofing is satisfied.

Lifetime Prediction of Wind Turbine Blade Based on Full-Scale Fatigue Testing

In order to predict the lifetime of products appropriately with long lifetime and high reliability,the accelerated degradation testing(ADT)has been proposed.Composite wind turbine blade is one of the most important components in wind turbine system.Its fatigue cycle is very long in practice.A full-scale fatigue testing is usually used to verify the design of a new blade.In general,the full-scale fatigue testing of blade is accelerated on the basis of the damage equivalent principle.During the full-scale fatigue test ing,blade is subjected to higher testing load than normal operat ing conditions;consequently,the performance degradation of the blade is hastened over time.The full-scale fatigue testing of blade is regarded as a special ADT.According to the fatigue failure criterion,we choose blade stiffness as the characteristic quantity of the blade performance,and propose an accelerated model(AM)for blade on the basis of the theories of ADT.Then,degradation path of the blade stiffness is modeled by using Gamma process.Finally,the lifet ime prediction of full-scale megawatt(MW)blade is conducted by combining the proposed AM and blade stiffness degradation model.The prediction results prove the reasonability and validity of this study.This can supply a new approach to predict the lifetime of the full-scale MW blade.

Study on smoke propagation in tunnel construction of a hydropower station: A full-scale fire experiment

In this study,full-scale fire experiments were conducted in a hydropower station to investigate smoke propagation during tunnel construction.The flame height,smoke temperature and stratification,smoke descent and spread velocity were analyzed via measurements and on-site observations.The initial combustion stage was largely affected by ignition source during tunnel construction for diesel pool fire,and the average flame height in the fully developed stage could reach 1.4-2.1 m in experimental fire scenarios.The gradient of the smoke temperature evolution near the fire was the opposite for the upstream and downstream regions.The longitudinal temperature distribution was concentrated in a small range at the heights of the smoke layer,and gradually decreased by air entrainment as the height decreased,while further increasing in the lower half of the tunnel height in the near-fire region under heat radiation from the fire source.Moreover,distinct and stable smoke stratification formed during the fully developed combustion stage,and the smoke layer interface was at approximately half the tunnel height.Smoke descent was aggravated in the decay stage of combustion,and the fire risk remained high after the fully developed period.The smoke front spread velocity was empirically determined for the full-scale tunnel fire scenarios.Conclusions from full-scale experiments can support smoke control design and on-site fire emergency response plans for hydropower stations.

高压涡轮盘螺栓孔疲劳模拟件设计及试验

航空发动机关键件采用模拟件开展试验可在一定程度上替代真实结构试验,从而大幅节省试验周期和成本。为满足某型发动机高压涡轮盘定寿需求,减少真实轮盘低循环疲劳的试验成本,本文采用考虑应力梯度影响的结构特征模拟件设计方法,设计了该发动机高压涡轮盘螺栓孔部位的结构特征模拟件,开展了特征模拟件及轮盘真实结构的低循环疲劳试验;对于模拟件试验结果,应用统计学方法得到了具有一定置信度和可靠度的模拟件寿命和分散度,采用该分散度计算得到的模拟件安全循环寿命和轮盘实际试验结果相比,模拟件安全循环寿命小于轮盘实际低循环疲劳寿命,误差为14.69%,该螺栓孔模拟件设计及低循环疲劳试验研究可用于指导实际轮盘的定寿工作,具有一定的工程参考价值。

表面肌电测试技术在研究生实验教学中的应用

利用表面肌电测试技术测量肌肉疲劳,开设研究型实验教学项目,让学生充分发挥主观能动性,独立设计实验方案,独立判断实验方案的合理性,以及运用基本实验技能进行实验操作和数据分析,熟练掌握表面肌电测试方法。该实验教学项目充实了兵器专业研究生的实验教学内容,能够培养学生的科学思维、创新精神和具体实验技能,为学生今后的科研和工作提供必要的实验手段。

卒中后疲劳患者疲劳体验及应对策略的质性研究

目的深入了解卒中后疲劳患者疲劳体验及应对策略,为制定针对性护理方案提供参考。方法采用描述性质性研究,按照目的抽样法选取16例卒中后疲劳患者进行半结构访谈,运用主题分析法对访谈资料进行分析与整理。结果卒中后疲劳患者疲劳体验共提炼出4个主题:卒中后疲劳特征、日常生活陷入紊乱状态、与他人讨论疲劳的反馈、渴望获得支持与理解。疲劳应对策略共提炼出2个主题:努力克服及适应疲劳、逃避或放弃应对疲劳。结论医护人员应重视卒中后疲劳患者的疲劳筛查与评估,鼓励患者正确应对疲劳,并采取多渠道的综合干预策略,缓解患者的疲劳症状。