In this paper, reliability analysis for the offshore jacket platform with the interaction of structure- pile- soil under extreme environmental loads is carried out. The inherent uncertainties of the environmental load...In this paper, reliability analysis for the offshore jacket platform with the interaction of structure- pile- soil under extreme environmental loads is carried out. The inherent uncertainties of the environmental load, foundation soil, platform itself, and calculating models are evaluated. The action of extreme loads on the offshore platform is modeled as a function of extreme wave height. The system capacity of the whole platform is determined by nonlinear pushover analysis, and the relevant probability property is obtained by the simulation method. The reliability model for the whole jacket platform is described as the relationship between the load and resistance based on the offshore design codes. The reliability of whole platform is calculated by the analytical method and the importance sampling method on the basis of a case study for a tripod jacket platform.展开更多
There has existed a great deal of theory researches in term of chip production and chip breaking characteristics under conventional cutting and high speed cutting conditions,however,there isn＇t sufficient research on...There has existed a great deal of theory researches in term of chip production and chip breaking characteristics under conventional cutting and high speed cutting conditions,however,there isn＇t sufficient research on chip formation mechanism as well as its influence on cutting state regarding large workpieces under extreme load cutting.This paper presents a model of large saw-tooth chip through applying finite element simulation method,which gives a profound analysis about the characteristics of the extreme load cutting as well as morphology and removal of the large chip.In the meantime,a calculation formula that gives a quantitative description of the saw-tooth level regarding the large chip is established on the basis of cutting experiments on high temperature and high strength steel2.25Cr-lMo-0.25V.The cutting experiments are carried out by using the scanning electron microscope and super depth of field electron microscope to measure and calculate the large chip produced under different cutting parameters,which can verify the validity of the established model.The calculating results show that the large saw-toothed chip is produced under the squeezing action between workpiece and cutting tools.In the meanwhile,the chip develops a hardened layer where contacts the cutting tool and the saw-tooth of the chip tend to form in transverse direction.This research creates the theoretical model for large chip and performs the cutting experiments under the extreme load cutting condition,as well as analyzes the production mechanism of the large chip in the macro and micro conditions.Therefore,the proposed research could provide theoretical guidance and technical support in improving productivity and cutting technology research.展开更多
Projectiles made of reactive structure materials(RSM)can damage the target with not only kinetic but also chemical energy,but the enhanced damage potential of RSM may become compromised if extreme loading condition di...Projectiles made of reactive structure materials(RSM)can damage the target with not only kinetic but also chemical energy,but the enhanced damage potential of RSM may become compromised if extreme loading condition disintegrates the projectile before the target is reached.In this work,a ductile coating of Ni was introduced to a tungsten-zirconium(W-Zr)alloy,a typical brittle RSM,to preserve the damage potential of the projectile.Detonation driving tests were carried out with X-ray photography and gunpowder deflagration driving tests were carried out with high-speed photography for the coated and uncoated RSM samples,respectively.The craters on the witness target were analyzed by scanning electron microscopy and X-ray diffraction.The Ni coating was found to effectively preserve the damage potential of the W-Zr alloy under extreme loading conditions,whereas the uncoated sample fractured and ignited before impacting the target in both detonation and deflagration driving.The crack propagation between the reactively brittle core and the ductile coating was analyzed based on the crack arrest theory to mechanistically demonstrate how the coating improves the structural integrity and preserves the damage potential of the projectile.Specifically,the Ni coating envelops theW-Zr core until the coated sphere penetrates the target,and the coating is then eroded and worn to release the reactive core for the projectile to damage the target more intensively.展开更多
Conducting bench tests for tractors according to the load spectrum is essential for assessing their reliability and fatigue durability.However,achieving an accurate replication of field operating conditions poses chal...Conducting bench tests for tractors according to the load spectrum is essential for assessing their reliability and fatigue durability.However,achieving an accurate replication of field operating conditions poses challenges due to the disparity in response characteristics between the tractor bench loading system and the frequency data of the load spectrum.Consequently,discrepancies in test results arise.To mitigate this challenge,this study proposes a loading method for the tractor rotary tillage load spectrum based on extreme load retention resampling.Firstly,a tractor rotary tillage load acquisition test was conducted,and a one-time-extrapolated load spectrum was compiled based on the Peak Over Threshold model.Considering the characteristics of rotary tillage operations,the tractor rotary tillage load spectrum loading bench was developed,which primarily includes the Power Take-Off(PTO)loading system and the suspension loading system.On this basis,a rotary tillage load spectrum loading system based on a Fuzzy-PID controller was proposed to realize the dynamic loading of the rotary tillage load spectrum.The dynamic response characteristics of the loading bench were analyzed based on a simulation model,and the results showed that the loading bench can achieve dynamic loading of load spectra with frequencies below 25 Hz.To match this characteristic,a load spectrum resampling method based on extreme load retention was proposed to resample the rotary tillage load spectrum.Based on the retention of the load spectrum fatigue damage,a resampled rotary tillage load spectrum with a resampling ratio of 3 was obtained,with a loading frequency of 20.98 Hz.Finally,the tractor rotary tillage loading test was conducted based on the resampled rotary tillage load spectrum.The test results demonstrated that the loading bench effectively replicated the resampled rotary tillage load spectrum.For the PTO torque load spectrum,the average error is–7.53%,with a delay of 30 ms,and for the suspension load spectrum,the average error is–2.48%,with a delay of 22 ms.The result indicated that the resampled load spectrum can well match the dynamic characteristics of the loading bench.This research can serve as a practical reference for implementing tractor bench tests grounded in load spectra.展开更多
In this study, the influence of opening parameters on the ultimate strength of perforated plates subjected to extreme cyclic loading in the presence of material kinematic hardening and isotro pic hardening was analyze...In this study, the influence of opening parameters on the ultimate strength of perforated plates subjected to extreme cyclic loading in the presence of material kinematic hardening and isotro pic hardening was analyzed. It is found that the ultimate strength of the perforated plates decreases rapidly and stabilizes in the first four cycles. Plates with oblong openings have a greater ultimate strength compared to plates with rectangular openings, while the relative strengthening ratio decreases over the duration of the cycle. The location of the openings is also an important parameter that affects the strength of the structure, as the plates with openings close to the edges in the longitudinal direction have higher strengths, while in the transverse direction the strengths are higher when the openings are close to the center. Among the three opening-strengthening methods compared, the Carling stiffener method maintains a better strengthening effect under cyclic loads for many periods.展开更多
The traffic condition of Taizhou Yangtze River Bridge is obtained to a certain extent, according to the traffic investigation nearby Taizhou Bridge. The statistical characteristics of the traffic conditions are acquir...The traffic condition of Taizhou Yangtze River Bridge is obtained to a certain extent, according to the traffic investigation nearby Taizhou Bridge. The statistical characteristics of the traffic conditions are acquired by statistical analysis. Simulation of the extreme vehicle loads and the sensitive analysis of load parameters are carried out based on these data complemented, which would guide the determination of the frictional coefficient between the main cables and the saddle.展开更多
Records of wave-induced damage on coastal bridges during natural hazards have been well documented over the past two decades.It is of utmost importance to decipher the loading mechanism and enhance the resilience of c...Records of wave-induced damage on coastal bridges during natural hazards have been well documented over the past two decades.It is of utmost importance to decipher the loading mechanism and enhance the resilience of coastal bridges during extreme wave-inducing events.Quantification of vulnerability of these structures is an essential step in designing a resilient bridge system.Recently,considerable efforts have been made to study the force applied and the response of coastal bridge systems during extreme wave loading conditions.Although remarkable progress can be found in the quantification of load and response of coastal superstructures,very few studies assessed coastal bridge resiliency against extreme wave-induced loads.This paper adopts a simplified and practical technique to analyze and assess the resilience of coastal bridges exposed to extreme waves.Component-level and system-level fragility analyses form the basis of the resiliency analysis where the recovery functions are adopted based on the damage levels.It is shown that wave period has the highest contribution to the variation of bridge resiliency.Moreover,this study presents the uncertainty quantification in resiliency variation due to changes in wave load intensity.Results show that the bridge resiliency becomes more uncertain as the intensity of wave parameters increases.Finally,possible restoration strategies based on the desired resilience level and the attitude of decision-makers are also discussed.展开更多
With the development of cutting-edge sciences and new technologies,we have to consider the size,the density,the hardness,the stiffness and other properties of engineering materials and structures beyond the convention...With the development of cutting-edge sciences and new technologies,we have to consider the size,the density,the hardness,the stiffness and other properties of engineering materials and structures beyond the conventional ranges,as well as their mechanical behavior in extreme environments,such as ultra-conventional temperature,speed,physical and chemical fields,and severe weather,and more effective theories and methods of mechanics are required.This paper first gives the fundamental definition and the scientific connotation of extreme mechanics,then reviews the studies of extreme mechanics from three aspects:the extreme properties,the extreme loads,and the discipline development,as well as major engineering and scientific challenges.The characteristics of extreme mechanics and major challenges in the aspects of mechanical theory,computational methods and experimental techniques are discussed.Prospectivei developments of extreme mechanics are suggested.展开更多
For the global and structural fatigue strength analysis of a semi-submersible platform, wave loads under design conditions are calculated by use of the three-dimensional boundary element method. Methods for calculatin...For the global and structural fatigue strength analysis of a semi-submersible platform, wave loads under design conditions are calculated by use of the three-dimensional boundary element method. Methods for calculating the forward-speed free-surface Green function are discussed and a computer program with this Green function is developed. According to the special rules, the wave loads under several typical design conditions of the platform are calculated. The maximum vertical bending moment, torsion moment and horizontal split force are determined from a series of contour maps of wave loads for the wave period of 5 to 18 seconds at a certain interval and the wave phase of 0degrees to 360degrees at a certain interval. The wave height is determined by the function of wave period with a given exceedance probability. The maximum wave loads under the combination of wave parameters are used as the input of hydrodynamic pressure in the three-dimensional finite element analysis process. The transfer functions of wave loads on the platform are used for the fatigue strength analysis of the K-tubular joint and the sub-model of the structure.展开更多
Within the context of global energy transitions,many wind turbines have been installed in desert and Gobi regions.Nevertheless,the impact of turbulence characteristics in actual sand-laden atmospheric flows on the aer...Within the context of global energy transitions,many wind turbines have been installed in desert and Gobi regions.Nevertheless,the impact of turbulence characteristics in actual sand-laden atmospheric flows on the aerodynamic performance of wind turbines has not been evaluated.The current study employs the high-quality wind velocity data measured in the Qingtu Lake Observation Array station of Min Qin to reveal the effects of turbulence characteristics in sand-laden atmospheric flows on the power and loads of a small wind turbine.The results demonstrate that turbulent coherent structures under sand-laden conditions occur more frequently and with shorter durations than that under the unladen conditions,leading to frequent and large fluctuations of wind turbine loads,specifically,the power,thrust,and blade root flapwise moment increased by 238%,167%,and 194%,respectively.The predictions by applying the extreme turbulence model suggested that the maximum extreme thrust,blade root flapwise moment,and blade root edgewise moment of wind turbine under sand-laden conditions are 23%,19%,and 7%higher than that under unladen conditions.This study is expected to provide a basic supply for wind turbine design and siting decisions in sand-laden environment.展开更多
As an attractive class of metallic materials,single-phase CrCoNi medium-entropy alloy(MEA)has drawn much attention recently regarding their deformation behaviors,but the dynamically mechanical responses of this alloy ...As an attractive class of metallic materials,single-phase CrCoNi medium-entropy alloy(MEA)has drawn much attention recently regarding their deformation behaviors,but the dynamically mechanical responses of this alloy at high strain rates remain less studied,especially coupled with extremely low temperatures.In this study,the dynamic deformation behaviors of this CrCoNi MEA were systematically investigated at room temperature(RT)of 298 K and liquid nitrogen temperature(LNT)of 77 K using the split Hopkinson pressure bar(SHPB).This alloy exhibited a combination of higher yield strength and stronger hardening rate upon dynamic compressive deformation when the loading conditions become much harsher(higher strain rate or lower temperature).Detailed microstructure analyses indicated that the strong strain hardening ability during dynamic deformation was mainly attributed to the continuous formation of nanoscale deformation twins.Furthermore,as loaded at LNT,multi-directional deformation twins were activated.Meanwhile,due to the interaction between Shockley partial dislocations and twin boundaries,large-sized deformation-induced FCC-HCP phase transformations at a micrometer scale were also observed within the grains,which not only accommodated the plasticity but also played an important role in improving the hardening capability owing to the appearance of newly generated interfaces.展开更多
In this study, the aerodynamic characteristics of tall buildings with corner modifications (e.g., local wind force coefficients, mean pressure distributions, normalized power spectrum density, and extreme local pressu...In this study, the aerodynamic characteristics of tall buildings with corner modifications (e.g., local wind force coefficients, mean pressure distributions, normalized power spectrum density, and extreme local pressure) were examined. Wind tunnel experiments were conducted to measure the wind pressures on building models with different heights and recessed corners of different ratios. At a wind direction of a = 0° (i.e., wind blowing on the front of a building), corner modifications effectively reduced wind forces in all cases. Specifically, small corner modification ratios reduced wind forces more effectively than their larger counterparts. However, corner modifications resulted in extreme local pressure on building surfaces. In addition, for small corner modification ratios, the probability of extreme local pressure occurring at a = 0° was high. This probability was also high for large corner modification ratios at a = 15° (i.e., wind blowing slightly obliquely on the front of a building) because wind blowing obliquely creates substantial vortex shedding on one side surface and extreme negative pressure over one building side surface. Results of computational fluid dynamic modeling were adopted to determine details of the aerodynamic characteristics of tall buildings with corner modifications.展开更多
Innovative features of wind turbine blades with flatback at inboard region,thick airfoils at inboard as well as mid-span region and transversely stepped thickness in spar caps have been proposed by Institute of Engine...Innovative features of wind turbine blades with flatback at inboard region,thick airfoils at inboard as well as mid-span region and transversely stepped thickness in spar caps have been proposed by Institute of Engineering Thermophysics,Chinese Academy of Sciences(IET-Wind)in order to improve both aerodynamic and structural efficiency of rotor blades.To verify the proposed design concepts,this study first presented numerical analysis using finite element method to clarify the effect of flatback on local buckling strength of the inboard region.Blade models with various loading cases,inboard configurations,and core materials were comparatively studied.Furthermore,a prototype blade incorporated with innovative features was manufactured and tested under static bending loads to investigate its structural response and characteristics.It was found that rotor blades with flatback exhibited favorable local buckling strength at the inboard region compared with those with conventional sharp trailing edge when low-density PVC foam was used.The prototype blade showed linear behavior under extreme loads in spar caps,aft panels,shear web and flatback near the maximum chord which is usually susceptible to buckling in the blades according to traditional designs.The inboard region of the blade showed exceptional load-carrying capacity as it survived420%extreme loads in the experiment.Through this study,potential structural advantages by applying proposed structural features to large composite blades of multi-megawatt wind turbines were addressed.展开更多
文摘In this paper, reliability analysis for the offshore jacket platform with the interaction of structure- pile- soil under extreme environmental loads is carried out. The inherent uncertainties of the environmental load, foundation soil, platform itself, and calculating models are evaluated. The action of extreme loads on the offshore platform is modeled as a function of extreme wave height. The system capacity of the whole platform is determined by nonlinear pushover analysis, and the relevant probability property is obtained by the simulation method. The reliability model for the whole jacket platform is described as the relationship between the load and resistance based on the offshore design codes. The reliability of whole platform is calculated by the analytical method and the importance sampling method on the basis of a case study for a tripod jacket platform.
基金Supported by National Natural Science Foundation of China(Grant No.51175131)
文摘There has existed a great deal of theory researches in term of chip production and chip breaking characteristics under conventional cutting and high speed cutting conditions,however,there isn＇t sufficient research on chip formation mechanism as well as its influence on cutting state regarding large workpieces under extreme load cutting.This paper presents a model of large saw-tooth chip through applying finite element simulation method,which gives a profound analysis about the characteristics of the extreme load cutting as well as morphology and removal of the large chip.In the meantime,a calculation formula that gives a quantitative description of the saw-tooth level regarding the large chip is established on the basis of cutting experiments on high temperature and high strength steel2.25Cr-lMo-0.25V.The cutting experiments are carried out by using the scanning electron microscope and super depth of field electron microscope to measure and calculate the large chip produced under different cutting parameters,which can verify the validity of the established model.The calculating results show that the large saw-toothed chip is produced under the squeezing action between workpiece and cutting tools.In the meanwhile,the chip develops a hardened layer where contacts the cutting tool and the saw-tooth of the chip tend to form in transverse direction.This research creates the theoretical model for large chip and performs the cutting experiments under the extreme load cutting condition,as well as analyzes the production mechanism of the large chip in the macro and micro conditions.Therefore,the proposed research could provide theoretical guidance and technical support in improving productivity and cutting technology research.
基金National Natural Science Foundation of China.Grant ID:11872123.
文摘Projectiles made of reactive structure materials(RSM)can damage the target with not only kinetic but also chemical energy,but the enhanced damage potential of RSM may become compromised if extreme loading condition disintegrates the projectile before the target is reached.In this work,a ductile coating of Ni was introduced to a tungsten-zirconium(W-Zr)alloy,a typical brittle RSM,to preserve the damage potential of the projectile.Detonation driving tests were carried out with X-ray photography and gunpowder deflagration driving tests were carried out with high-speed photography for the coated and uncoated RSM samples,respectively.The craters on the witness target were analyzed by scanning electron microscopy and X-ray diffraction.The Ni coating was found to effectively preserve the damage potential of the W-Zr alloy under extreme loading conditions,whereas the uncoated sample fractured and ignited before impacting the target in both detonation and deflagration driving.The crack propagation between the reactively brittle core and the ductile coating was analyzed based on the crack arrest theory to mechanistically demonstrate how the coating improves the structural integrity and preserves the damage potential of the projectile.Specifically,the Ni coating envelops theW-Zr core until the coated sphere penetrates the target,and the coating is then eroded and worn to release the reactive core for the projectile to damage the target more intensively.
基金supported by the Basic Research Plan of Shanxi Province(Grant No.202203021212158)the National Key Laboratory Construction Project of Intelligent Agricultural Power Equipment(Grant No.2024AC047)the National Natural Science Foundation of China(Grant No.62404208 and 32301719).
文摘Conducting bench tests for tractors according to the load spectrum is essential for assessing their reliability and fatigue durability.However,achieving an accurate replication of field operating conditions poses challenges due to the disparity in response characteristics between the tractor bench loading system and the frequency data of the load spectrum.Consequently,discrepancies in test results arise.To mitigate this challenge,this study proposes a loading method for the tractor rotary tillage load spectrum based on extreme load retention resampling.Firstly,a tractor rotary tillage load acquisition test was conducted,and a one-time-extrapolated load spectrum was compiled based on the Peak Over Threshold model.Considering the characteristics of rotary tillage operations,the tractor rotary tillage load spectrum loading bench was developed,which primarily includes the Power Take-Off(PTO)loading system and the suspension loading system.On this basis,a rotary tillage load spectrum loading system based on a Fuzzy-PID controller was proposed to realize the dynamic loading of the rotary tillage load spectrum.The dynamic response characteristics of the loading bench were analyzed based on a simulation model,and the results showed that the loading bench can achieve dynamic loading of load spectra with frequencies below 25 Hz.To match this characteristic,a load spectrum resampling method based on extreme load retention was proposed to resample the rotary tillage load spectrum.Based on the retention of the load spectrum fatigue damage,a resampled rotary tillage load spectrum with a resampling ratio of 3 was obtained,with a loading frequency of 20.98 Hz.Finally,the tractor rotary tillage loading test was conducted based on the resampled rotary tillage load spectrum.The test results demonstrated that the loading bench effectively replicated the resampled rotary tillage load spectrum.For the PTO torque load spectrum,the average error is–7.53%,with a delay of 30 ms,and for the suspension load spectrum,the average error is–2.48%,with a delay of 22 ms.The result indicated that the resampled load spectrum can well match the dynamic characteristics of the loading bench.This research can serve as a practical reference for implementing tractor bench tests grounded in load spectra.
文摘In this study, the influence of opening parameters on the ultimate strength of perforated plates subjected to extreme cyclic loading in the presence of material kinematic hardening and isotro pic hardening was analyzed. It is found that the ultimate strength of the perforated plates decreases rapidly and stabilizes in the first four cycles. Plates with oblong openings have a greater ultimate strength compared to plates with rectangular openings, while the relative strengthening ratio decreases over the duration of the cycle. The location of the openings is also an important parameter that affects the strength of the structure, as the plates with openings close to the edges in the longitudinal direction have higher strengths, while in the transverse direction the strengths are higher when the openings are close to the center. Among the three opening-strengthening methods compared, the Carling stiffener method maintains a better strengthening effect under cyclic loads for many periods.
基金National Science and Technology Support Program of China ( No. 2009BAG15B02)Key Pro-grams for Science and Technology Development of Chinese Transportation Industry( No. 2008-353-332-180)
文摘The traffic condition of Taizhou Yangtze River Bridge is obtained to a certain extent, according to the traffic investigation nearby Taizhou Bridge. The statistical characteristics of the traffic conditions are acquired by statistical analysis. Simulation of the extreme vehicle loads and the sensitive analysis of load parameters are carried out based on these data complemented, which would guide the determination of the frictional coefficient between the main cables and the saddle.
基金sponsored by the Natural Science and Engineering Research Council(NSERC)of Canada through the Discovery Grant and additional funding provided by University of Calgary through the start-up grant.
文摘Records of wave-induced damage on coastal bridges during natural hazards have been well documented over the past two decades.It is of utmost importance to decipher the loading mechanism and enhance the resilience of coastal bridges during extreme wave-inducing events.Quantification of vulnerability of these structures is an essential step in designing a resilient bridge system.Recently,considerable efforts have been made to study the force applied and the response of coastal bridge systems during extreme wave loading conditions.Although remarkable progress can be found in the quantification of load and response of coastal superstructures,very few studies assessed coastal bridge resiliency against extreme wave-induced loads.This paper adopts a simplified and practical technique to analyze and assess the resilience of coastal bridges exposed to extreme waves.Component-level and system-level fragility analyses form the basis of the resiliency analysis where the recovery functions are adopted based on the damage levels.It is shown that wave period has the highest contribution to the variation of bridge resiliency.Moreover,this study presents the uncertainty quantification in resiliency variation due to changes in wave load intensity.Results show that the bridge resiliency becomes more uncertain as the intensity of wave parameters increases.Finally,possible restoration strategies based on the desired resilience level and the attitude of decision-makers are also discussed.
文摘With the development of cutting-edge sciences and new technologies,we have to consider the size,the density,the hardness,the stiffness and other properties of engineering materials and structures beyond the conventional ranges,as well as their mechanical behavior in extreme environments,such as ultra-conventional temperature,speed,physical and chemical fields,and severe weather,and more effective theories and methods of mechanics are required.This paper first gives the fundamental definition and the scientific connotation of extreme mechanics,then reviews the studies of extreme mechanics from three aspects:the extreme properties,the extreme loads,and the discipline development,as well as major engineering and scientific challenges.The characteristics of extreme mechanics and major challenges in the aspects of mechanical theory,computational methods and experimental techniques are discussed.Prospectivei developments of extreme mechanics are suggested.
文摘For the global and structural fatigue strength analysis of a semi-submersible platform, wave loads under design conditions are calculated by use of the three-dimensional boundary element method. Methods for calculating the forward-speed free-surface Green function are discussed and a computer program with this Green function is developed. According to the special rules, the wave loads under several typical design conditions of the platform are calculated. The maximum vertical bending moment, torsion moment and horizontal split force are determined from a series of contour maps of wave loads for the wave period of 5 to 18 seconds at a certain interval and the wave phase of 0degrees to 360degrees at a certain interval. The wave height is determined by the function of wave period with a given exceedance probability. The maximum wave loads under the combination of wave parameters are used as the input of hydrodynamic pressure in the three-dimensional finite element analysis process. The transfer functions of wave loads on the platform are used for the fatigue strength analysis of the K-tubular joint and the sub-model of the structure.
基金supported by the National Natural Science Foundation of China(Grant Nos.52276197 and 52166014)Gansu Province Key Research and Development Program-Industrial Project(Grant No.23YFGA0069)the National Key Research and Development Plan(Grant No.20t22YFB4202102-04).
文摘Within the context of global energy transitions,many wind turbines have been installed in desert and Gobi regions.Nevertheless,the impact of turbulence characteristics in actual sand-laden atmospheric flows on the aerodynamic performance of wind turbines has not been evaluated.The current study employs the high-quality wind velocity data measured in the Qingtu Lake Observation Array station of Min Qin to reveal the effects of turbulence characteristics in sand-laden atmospheric flows on the power and loads of a small wind turbine.The results demonstrate that turbulent coherent structures under sand-laden conditions occur more frequently and with shorter durations than that under the unladen conditions,leading to frequent and large fluctuations of wind turbine loads,specifically,the power,thrust,and blade root flapwise moment increased by 238%,167%,and 194%,respectively.The predictions by applying the extreme turbulence model suggested that the maximum extreme thrust,blade root flapwise moment,and blade root edgewise moment of wind turbine under sand-laden conditions are 23%,19%,and 7%higher than that under unladen conditions.This study is expected to provide a basic supply for wind turbine design and siting decisions in sand-laden environment.
基金supported by the National Natural Science Foundation of China(Grant No.12102363)the China National Funds for Distinguished Young Scientists(Grant No.12025205).
文摘As an attractive class of metallic materials,single-phase CrCoNi medium-entropy alloy(MEA)has drawn much attention recently regarding their deformation behaviors,but the dynamically mechanical responses of this alloy at high strain rates remain less studied,especially coupled with extremely low temperatures.In this study,the dynamic deformation behaviors of this CrCoNi MEA were systematically investigated at room temperature(RT)of 298 K and liquid nitrogen temperature(LNT)of 77 K using the split Hopkinson pressure bar(SHPB).This alloy exhibited a combination of higher yield strength and stronger hardening rate upon dynamic compressive deformation when the loading conditions become much harsher(higher strain rate or lower temperature).Detailed microstructure analyses indicated that the strong strain hardening ability during dynamic deformation was mainly attributed to the continuous formation of nanoscale deformation twins.Furthermore,as loaded at LNT,multi-directional deformation twins were activated.Meanwhile,due to the interaction between Shockley partial dislocations and twin boundaries,large-sized deformation-induced FCC-HCP phase transformations at a micrometer scale were also observed within the grains,which not only accommodated the plasticity but also played an important role in improving the hardening capability owing to the appearance of newly generated interfaces.
基金This work was supported by Korea Research Fellowship Program through the National Research Foundation of Korea(NRF)funded by the Ministry of Science and ICT。
文摘In this study, the aerodynamic characteristics of tall buildings with corner modifications (e.g., local wind force coefficients, mean pressure distributions, normalized power spectrum density, and extreme local pressure) were examined. Wind tunnel experiments were conducted to measure the wind pressures on building models with different heights and recessed corners of different ratios. At a wind direction of a = 0° (i.e., wind blowing on the front of a building), corner modifications effectively reduced wind forces in all cases. Specifically, small corner modification ratios reduced wind forces more effectively than their larger counterparts. However, corner modifications resulted in extreme local pressure on building surfaces. In addition, for small corner modification ratios, the probability of extreme local pressure occurring at a = 0° was high. This probability was also high for large corner modification ratios at a = 15° (i.e., wind blowing slightly obliquely on the front of a building) because wind blowing obliquely creates substantial vortex shedding on one side surface and extreme negative pressure over one building side surface. Results of computational fluid dynamic modeling were adopted to determine details of the aerodynamic characteristics of tall buildings with corner modifications.
基金supported by the National Natural Science Foundation of China(Grant No.51405468)
文摘Innovative features of wind turbine blades with flatback at inboard region,thick airfoils at inboard as well as mid-span region and transversely stepped thickness in spar caps have been proposed by Institute of Engineering Thermophysics,Chinese Academy of Sciences(IET-Wind)in order to improve both aerodynamic and structural efficiency of rotor blades.To verify the proposed design concepts,this study first presented numerical analysis using finite element method to clarify the effect of flatback on local buckling strength of the inboard region.Blade models with various loading cases,inboard configurations,and core materials were comparatively studied.Furthermore,a prototype blade incorporated with innovative features was manufactured and tested under static bending loads to investigate its structural response and characteristics.It was found that rotor blades with flatback exhibited favorable local buckling strength at the inboard region compared with those with conventional sharp trailing edge when low-density PVC foam was used.The prototype blade showed linear behavior under extreme loads in spar caps,aft panels,shear web and flatback near the maximum chord which is usually susceptible to buckling in the blades according to traditional designs.The inboard region of the blade showed exceptional load-carrying capacity as it survived420%extreme loads in the experiment.Through this study,potential structural advantages by applying proposed structural features to large composite blades of multi-megawatt wind turbines were addressed.
