Traditional gust load factor(GLF)method,inertial wind load(IWL)method and tri-component method(LRC+IWL)cannot accurately analyze the wind-induced responses of super-large cooling towers,so the real combination formula...Traditional gust load factor(GLF)method,inertial wind load(IWL)method and tri-component method(LRC+IWL)cannot accurately analyze the wind-induced responses of super-large cooling towers,so the real combination formulas of fluctuating wind-induced responses and equivalent static wind loads(ESWLSs)were derived based on structural dynamics and random vibration theory.The consistent coupled method(CCM)was presented to compensate the coupled term between background and resonant response.Taking the super-large cooling tower(H=215 m)of nuclear power plant in Jiangxi Province,China,which is the highest and largest in China,as the example,based on modified equivalent beam-net design method,the aero-elastic model for simultaneous pressure and vibration measurement of super-large cooling tower is firstly carried out.Then,combining wind tunnel test and CCM,the effects of self-excited force on the surface pressures and wind-induced responses are discussed,and the wind-induced response characteristics of background component,resonant component,coupled term between background and resonant response,fluctuating responses,and wind vibration coefficients are discussed.It can be concluded that wind-induced response mechanism must be understood to direct the wind resistant design for super-large cooling towers.展开更多
To study the additional aerodynamic effect on a bridge girder under the action of wind-driven rain, the rainfall similarity considering raindrop impact and surface water is first given. Then, the dynamic characteristi...To study the additional aerodynamic effect on a bridge girder under the action of wind-driven rain, the rainfall similarity considering raindrop impact and surface water is first given. Then, the dynamic characteristics and the process of vortex and flutter generation of the segment models under different rain intensities and angles of attack are tested by considering several typical main girder sections as examples. The test results indicate that the start and end wind speeds,interval length and number of vortex vibrations remain unchanged when it is raining, rainfall will reduce the windinduced vortex response. When test rain intensity is large, the decrease of amplitude is obvious. However, after considering the rain intensity similarity in this study, all of actual maximum rain intensities after conversion approach the domestic extreme rain intensity of approximately 709 mm/h. It can be observed that rainfall has a limited influence on the dynamic characteristics of the structure and vortex vibration response. When the test rain intensity is 120 mm/h, the critical wind speed of the model flutter increases by 20%-30%. However, after considering the rain intensity similarity ratio, the influence of rainfall on the wind-induced flutter instability of the bridge girder may be ignored.展开更多
This paper mainly focuses on the establishment of an effective static estimation method for the extreme wind-induced force for clips between purlins and metal panels of the standing-seam metal roofing system(hereinaft...This paper mainly focuses on the establishment of an effective static estimation method for the extreme wind-induced force for clips between purlins and metal panels of the standing-seam metal roofing system(hereinafter referred to as SMRS)of typical double-slope light-weight steel portal frame structure considering dynamic characteristics of wind and structure.First,simultaneous pressure measurement with rigid gable roof models was conducted mainly considering the length-span ratio in the boundary layer wind tunnel of Tokyo Polytechnic University,Japan.Then,finite element modeling for SMRS according to the wind load path in the roofing system was carried out to check the actual wind load of the clips based on the traditional calculation method provided in design codes,and the spatial correlation of fluctuating wind pressure on the roof surface,as well as the dynamic effect of the roof structure itself,had been considered.According to the related Chinese,American,and Japanese codes,a magnification coefficient based on the traditional method of static wind-induced force for the clips was calculated and compared.Finally,a simplified estimation method of effective wind-induced force for the clips in typical zones on the roof surface considering dynamic characteristics was proposed.展开更多
Tuned mass dampers （TMDs） have been widely used in recent years to mitigate structural vibration. However, the damping mechanisms employed in the TMDs are mostly based on viscous dampers, which have several well-kno...Tuned mass dampers （TMDs） have been widely used in recent years to mitigate structural vibration. However, the damping mechanisms employed in the TMDs are mostly based on viscous dampers, which have several well-known disadvantages, such as oil leakage and difficult adjustment of damping ratio for an operating TMD. Alternatively, eddy current damping （ECD） that does not require any contact with the main structure is a potential solution. This paper discusses the design, analysis, manufacture and testing of a large-scale horizontal TMD based on ECD. First, the theoretical model of ECD is formulated, then one large-scale horizontal TMD using ECD is constructed, and finally performance tests of the TMD are conducted. The test results show that the proposed TMD has a very low intrinsic damping ratio, while the damping ratio due to ECD is the dominant damping source, which can be as large as 15% in a proper configuration. In addition, the damping ratios estimated with the theoretical model are roughly consistent with those identified from the test results, and the source of this error is investigated. Moreover, it is demonstrated that the damping ratio in the proposed TMD can be easily adjusted by varying the air gap between permanent magnets and conductive plates. In view of practical applications, possible improvements and feasibility considerations for the proposed TMD are then discussed. It is confirmed that the proposed TMD with ECD is reliable and feasible for use in structural vibration control.展开更多
The 2-dimensional unsteady aerodynamic forces,in the context of both a thin airfoil where theory of potential flow is always applicable and a bluff bridge-deck section where separated flow is typically induced,are inv...The 2-dimensional unsteady aerodynamic forces,in the context of both a thin airfoil where theory of potential flow is always applicable and a bluff bridge-deck section where separated flow is typically induced,are investigated from a point of view of whether or not they conform to the principle of linear superposition in situations of various structural motions and wind gusts.It is shown that some basic preconditions that lead to the linear superposability of the unsteady aerodynamic forces in cases of thin airfoil sections are no longer valid for a bluff section.Theoretical models of bridge aerodynamics such as the one related to flutter-buffeting analysis and those concerning aerodynamic admittance(AA)functions,however,necessitate implicitly this superposability.The contradiction revealed in this work may throw light on the perplexing problem of AA functions pertaining to the description of buffeting loads of bridge decks.Some existing theoretical AA models derived from flutter derivatives according to interrelations valid only for thin airfoil theories,which have been employed rather extensively in bridge aerodynamics,are demonstrated to be illogical.Finally,with full understanding of the preconditions of the applicability of linear superposability of the unsteady aerodynamic forces,suggestions in regard to experiment-based AA functions are presented.展开更多
A high-order direct numerical simulation of flow transition over a flat-plate at a free stream Mach number 0.5 is carried out. Formation and development of three-dimensional vortical structures, typically shown as λ-...A high-order direct numerical simulation of flow transition over a flat-plate at a free stream Mach number 0.5 is carried out. Formation and development of three-dimensional vortical structures, typically shown as λ-vortices, hairpin vortices and ring-like vortices, are observed. Numerical results show that there is a strong downdraft motion of fluid excited by every ring-like vortex in the late-stage of the transition process. At two sides of the vortical structure centerline, the downdraft motions induced by the ring-like vortex and the rotating legs superimpose. This is responsible for the appearance of a high-speed streak associated with the positive spike observed in a previous investigation and the appearance of a high-shear layer in the near wall region.展开更多
Mean wind response induced incompatibility and nonlinearity in bridge aerodynamics is discussed,where the mean wind and aeroelastic loads are applied simultaneously in time domain.A kind of incompatibility is found du...Mean wind response induced incompatibility and nonlinearity in bridge aerodynamics is discussed,where the mean wind and aeroelastic loads are applied simultaneously in time domain.A kind of incompatibility is found during the simultaneous simulation of the mean wind and aeroelastic loads,which leads to incorrect mean wind structural responses.It is found that the mathematic expectations (or Iimiting characteristics) of the aeroelastic models are fundamental to this kind of incompatibility.In this paper,two aeroelastic models are presented and discussed,one of indicial-function-denoted (IF-denoted) and another of rational-function-denoted (RF-denoted).It is shown that,in cases of low wind speeds,the IF-denoted model reflects correctly the mean wind load properties,and results in correct mean structural responses;in contrast,the RF-denoted model leads to incorrect mean responses due to its nonphysical mean properties.At very high wind speeds,however,even the IF-denoted model can lead to significant deviation from the correct response due to steady aerodynamic nonlinearity.To solve the incompatibility at high wind speeds,a methodology of subtraction of pseudo-steady effects from the aeroelastic model is put forward in this work.Finally,with the method presented,aeroelastic nonlinearity resulted from the mean wind response is investigated at both moderate and high wind speeds.展开更多
Slope variation will significantly affect the characteristics of the wind field around a hill.This paper conducts a large-eddy simulation(LES)on an ideal 3D hill to study the impact of slope on wind field properties.E...Slope variation will significantly affect the characteristics of the wind field around a hill.This paper conducts a large-eddy simulation(LES)on an ideal 3D hill to study the impact of slope on wind field properties.Eight slopes ranging from 10°to 45°at 5°intervals are considered,which covers most conventional hill slopes.The inflow turbulence for the LES is generated by adopting a modified generation method that combines the equilibrium boundary conditions with the Fluent inherent vortex method to improve the simulation accuracy.The time-averaged flow field and the instantaneous vortex structure under the eight slopes are comparatively analyzed.The accuracy of the present method is verified by comparison with experimental data.The slope can affect both the mean and fluctuating wind flow fields around the 3D hill,especially on the hilltop and the leeward side,where a critical slope of 25°can be observed.The fluctuating wind speeds at the tops of steep hills(with slope angles beyond 25°)decrease with increasing slope,while the opposite phenomenon occurs on gentle hills.With increasing slope,the energy of the high-speed descending airflow is enhanced and pushes the separated flow closer to the hill surface,resulting in increased wind speed near the wall boundary on the leeward side and inhibiting the development of turbulence.The vortex shedding trajectory in the wake region becomes wider and longer,suppressing the growth of the mean wind near the wall boundary and enhancing the turbulence intensity.展开更多
Complicated terrain was considered and simplified as two-dimensional(2D)terrain in a dynamical downscaling model and a parametric wind field model for typhoons developed by the Shanghai Typhoon Institute.The 2D terrai...Complicated terrain was considered and simplified as two-dimensional(2D)terrain in a dynamical downscaling model and a parametric wind field model for typhoons developed by the Shanghai Typhoon Institute.The 2D terrain was further modeled as uphill and downhill segments with various slope angles relative to the incoming flow.The wind speed ratios and pressure characteristics around the 2D terrain were numerically and experimentally investigated in this study.Aerodynamic characteristics of the 2D terrain with a limitedlength upper surface were first investigated in the wind tunnel with sheared incoming flow.The corresponding numerical investigation was also conducted by using the commercial computational fluid dynamics code FLUENT with the realizable k-ε turbulence model.Special efforts were made to maintain the inflow boundary conditions throughout the computational domain.Aerodynamic characteristics were then investigated for the ideal 2D terrain with an unlimited-length upper surface by using a numerical method with uniform incoming flow.Comparisons of the different terrain models and incoming flows from the above studies show that the wind pressure coefficients and the wind speed ratios are both affected by the slope angle.A negative peak value of the wind pressure coefficients exists at the escarpment point,where flow separation occurs,for the uphill and downhill terrain models with slope angles of 40°and 30°,respectively.Correspondingly,the streamwise wind speed ratios at the points above the escarpment point for the uphill terrain model increase with increasing slope angle,reach their peak values at the slope angle of a=40°and decrease when the slope angle increases further.For the downhill terrain model,similar trends exist at the points above the escarpment point with the exception that the critical slope angle is a=30°.展开更多
Based on the spatial model,a reliable and accurate calculation method on the shape finding of self anchored suspension bridge with spatial cables was studiedin this paper.On the principle that the shape of the main ca...Based on the spatial model,a reliable and accurate calculation method on the shape finding of self anchored suspension bridge with spatial cables was studiedin this paper.On the principle that the shape of the main cables between hangers is catenary,the iteration method of calculating the shapes of the spatial main cables under the load of hanger forces was deduced.The reasonable position of the saddle was determined according to the shape and the theoretical joint point of the main cables.The shapes of the main cables at completed cable stage werecalculated based on the unchanging principle of the zero-stress lengths of the main cables.By using a numerical method combining with the finite element method,one self-anchored suspension bridge with spatial cables was analyzed.The zero-stress length of the main cables,the position of the saddle,and the pre-offsetting of the saddle of the self-anchored suspension bridge were given.The reasonable shapes of the main cables at bridge completion stage and completed cable stage were presented.The results show that the shape-finding calculation method is effective and reliable.展开更多
Flutter derivatives are essential for flutter analysis of long-span bridges,and they are generally identified from the vibration testing data of a sectional model suspended in a wind tunnel.Making use of the forced vi...Flutter derivatives are essential for flutter analysis of long-span bridges,and they are generally identified from the vibration testing data of a sectional model suspended in a wind tunnel.Making use of the forced vibration testing data of three sectional models,namely,a thin-plate model,a nearly streamlined model,and a bluff-body model,a comparative study was made to identify the flutter derivatives of each model by using a time-domain method and a frequency-domain method.It was shown that all the flutter derivatives of the thin-plate model identified with the frequency-domain method and time-domain method,respectively,agree very well.Moreover,some of the flutter derivatives of each of the other two models identified with the two methods deviate to some extent.More precisely,the frequency-domain method usually results in smooth curves of the flutter derivatives.The formulation of time-domain method makes the identification results of flutter derivatives relatively sensitive to the signal phase lag between vibration state vector and aerodynamic forces and also prone to be disturbed by noise and nonlinearity.展开更多
The aerodynamic interference effects on aero-static coefficients of twin deck bridges with large span were investigated in detail by means of wind tunnel test.The distances between the twin decks and wind attack angle...The aerodynamic interference effects on aero-static coefficients of twin deck bridges with large span were investigated in detail by means of wind tunnel test.The distances between the twin decks and wind attack angles were changed during the wind tunnel test to study the effects on aerodynamic interferences of aerostatic coefficients of twin decks.The research results have shown that the drag coefficients of the leeward deck are much smaller than that of a single leeward deck.The drag coefficients of a windward deck decrease slightly com-pared with that of a single deck.The lift and torque coefficients of windward and leeward decks are also affected slightly by the aerodynamic interference of twin decks.And the aerodynamic interference effects on lift and torque coefficients of twin decks can be neglected.展开更多
An indoor thermal environment is affected by various heat elements,such as heat transfer through walls,solar radiation,and heat emissions from people,lighting and equipment.To promote both local thermal comfort and bu...An indoor thermal environment is affected by various heat elements,such as heat transfer through walls,solar radiation,and heat emissions from people,lighting and equipment.To promote both local thermal comfort and building energy efficiency,demand-oriented ventilation(such as personalized ventilation)has been developed.When using this method,a good understanding on indoor temperature distribution becomes necessary.For this purpose,an index known as Contribution Ratio of Indoor Climate(CRI)has been developed through extraction from the calculation results of Computational Fluid Dynamics(CFD).This index can be used to analyze the independent contribution of each heat element to indoor temperature distribution.In this paper,a complete and detailed introduction of the CRI is given,including its basic premises,definitions,and mathematical meaning.Particularly,calculation method of the CRI in natural convection airflow fields is further developed.Two cases(forced and natural convection airflow fields)have been carried out in different scenarios,with results showing that the CRI of a heat source had higher values in the area around itself.Also,it had a larger influence range in forced convection airflow field because of the convective airflow,while relatively larger CRI values only appear in the area above the heat source in the natural convection airflow field because of the heat plume.As a useful index for understanding the form of indoor temperature field,the CRI has guiding significance for regulating air-conditioning/ventilation systems to build better indoor thermal environment.展开更多
基金Projects(50978203,51208254)supported by the National Natural Science Foundation of ChinaProject(BK2012390)supported by Natural Science Foundation of Jiangsu Province,ChinaProject supported by the Priority Academic Program Development of Jiangsu Higher Education Institutions,China
文摘Traditional gust load factor(GLF)method,inertial wind load(IWL)method and tri-component method(LRC+IWL)cannot accurately analyze the wind-induced responses of super-large cooling towers,so the real combination formulas of fluctuating wind-induced responses and equivalent static wind loads(ESWLSs)were derived based on structural dynamics and random vibration theory.The consistent coupled method(CCM)was presented to compensate the coupled term between background and resonant response.Taking the super-large cooling tower(H=215 m)of nuclear power plant in Jiangxi Province,China,which is the highest and largest in China,as the example,based on modified equivalent beam-net design method,the aero-elastic model for simultaneous pressure and vibration measurement of super-large cooling tower is firstly carried out.Then,combining wind tunnel test and CCM,the effects of self-excited force on the surface pressures and wind-induced responses are discussed,and the wind-induced response characteristics of background component,resonant component,coupled term between background and resonant response,fluctuating responses,and wind vibration coefficients are discussed.It can be concluded that wind-induced response mechanism must be understood to direct the wind resistant design for super-large cooling towers.
基金Projects(20B062,19B054)supported by Excellent Youth Program of Hunan Education Department,ChinaProject(2019JJ50688)supported by Hunan Provincial Natural Science Foundation of ChinaProject(kq195004)supported by Changsha Science and Technology Bureau Project,China。
文摘To study the additional aerodynamic effect on a bridge girder under the action of wind-driven rain, the rainfall similarity considering raindrop impact and surface water is first given. Then, the dynamic characteristics and the process of vortex and flutter generation of the segment models under different rain intensities and angles of attack are tested by considering several typical main girder sections as examples. The test results indicate that the start and end wind speeds,interval length and number of vortex vibrations remain unchanged when it is raining, rainfall will reduce the windinduced vortex response. When test rain intensity is large, the decrease of amplitude is obvious. However, after considering the rain intensity similarity in this study, all of actual maximum rain intensities after conversion approach the domestic extreme rain intensity of approximately 709 mm/h. It can be observed that rainfall has a limited influence on the dynamic characteristics of the structure and vortex vibration response. When the test rain intensity is 120 mm/h, the critical wind speed of the model flutter increases by 20%-30%. However, after considering the rain intensity similarity ratio, the influence of rainfall on the wind-induced flutter instability of the bridge girder may be ignored.
基金financial support of the National Key Research and Development Program of China(No.2017YFC0703803)the Joint Usage/Research Center(JURC)project“Wind-induced Load Estimation for Clips of Standing-seam Roofing System Considering Dynamic Characteristics”from Tokyo Polytechnic University(2018 FY)the National Natural Science Foundation of China(Grant No.51978500).
文摘This paper mainly focuses on the establishment of an effective static estimation method for the extreme wind-induced force for clips between purlins and metal panels of the standing-seam metal roofing system(hereinafter referred to as SMRS)of typical double-slope light-weight steel portal frame structure considering dynamic characteristics of wind and structure.First,simultaneous pressure measurement with rigid gable roof models was conducted mainly considering the length-span ratio in the boundary layer wind tunnel of Tokyo Polytechnic University,Japan.Then,finite element modeling for SMRS according to the wind load path in the roofing system was carried out to check the actual wind load of the clips based on the traditional calculation method provided in design codes,and the spatial correlation of fluctuating wind pressure on the roof surface,as well as the dynamic effect of the roof structure itself,had been considered.According to the related Chinese,American,and Japanese codes,a magnification coefficient based on the traditional method of static wind-induced force for the clips was calculated and compared.Finally,a simplified estimation method of effective wind-induced force for the clips in typical zones on the roof surface considering dynamic characteristics was proposed.
基金State Key Program of Natural Science Foundation of China Under Grant No.50738002
文摘Tuned mass dampers （TMDs） have been widely used in recent years to mitigate structural vibration. However, the damping mechanisms employed in the TMDs are mostly based on viscous dampers, which have several well-known disadvantages, such as oil leakage and difficult adjustment of damping ratio for an operating TMD. Alternatively, eddy current damping （ECD） that does not require any contact with the main structure is a potential solution. This paper discusses the design, analysis, manufacture and testing of a large-scale horizontal TMD based on ECD. First, the theoretical model of ECD is formulated, then one large-scale horizontal TMD using ECD is constructed, and finally performance tests of the TMD are conducted. The test results show that the proposed TMD has a very low intrinsic damping ratio, while the damping ratio due to ECD is the dominant damping source, which can be as large as 15% in a proper configuration. In addition, the damping ratios estimated with the theoretical model are roughly consistent with those identified from the test results, and the source of this error is investigated. Moreover, it is demonstrated that the damping ratio in the proposed TMD can be easily adjusted by varying the air gap between permanent magnets and conductive plates. In view of practical applications, possible improvements and feasibility considerations for the proposed TMD are then discussed. It is confirmed that the proposed TMD with ECD is reliable and feasible for use in structural vibration control.
基金Projects(51178182,90915002)supported by the National Natural Science Foundation of ChinaProject(SLDRCE10-MB-03)supported by the Open Project of the State Key Laboratory of Disaster Reduction in Civil Engineering,China
文摘The 2-dimensional unsteady aerodynamic forces,in the context of both a thin airfoil where theory of potential flow is always applicable and a bluff bridge-deck section where separated flow is typically induced,are investigated from a point of view of whether or not they conform to the principle of linear superposition in situations of various structural motions and wind gusts.It is shown that some basic preconditions that lead to the linear superposability of the unsteady aerodynamic forces in cases of thin airfoil sections are no longer valid for a bluff section.Theoretical models of bridge aerodynamics such as the one related to flutter-buffeting analysis and those concerning aerodynamic admittance(AA)functions,however,necessitate implicitly this superposability.The contradiction revealed in this work may throw light on the perplexing problem of AA functions pertaining to the description of buffeting loads of bridge decks.Some existing theoretical AA models derived from flutter derivatives according to interrelations valid only for thin airfoil theories,which have been employed rather extensively in bridge aerodynamics,are demonstrated to be illogical.Finally,with full understanding of the preconditions of the applicability of linear superposability of the unsteady aerodynamic forces,suggestions in regard to experiment-based AA functions are presented.
基金Supported by the National Natural Science Foundation of China under Grant No 50738002, and AFOSR under Grant No FA9550-08-1-0201.
文摘A high-order direct numerical simulation of flow transition over a flat-plate at a free stream Mach number 0.5 is carried out. Formation and development of three-dimensional vortical structures, typically shown as λ-vortices, hairpin vortices and ring-like vortices, are observed. Numerical results show that there is a strong downdraft motion of fluid excited by every ring-like vortex in the late-stage of the transition process. At two sides of the vortical structure centerline, the downdraft motions induced by the ring-like vortex and the rotating legs superimpose. This is responsible for the appearance of a high-speed streak associated with the positive spike observed in a previous investigation and the appearance of a high-shear layer in the near wall region.
基金the National Natural Science Foundation of China(Grant No.51178182 and 51578233).
文摘Mean wind response induced incompatibility and nonlinearity in bridge aerodynamics is discussed,where the mean wind and aeroelastic loads are applied simultaneously in time domain.A kind of incompatibility is found during the simultaneous simulation of the mean wind and aeroelastic loads,which leads to incorrect mean wind structural responses.It is found that the mathematic expectations (or Iimiting characteristics) of the aeroelastic models are fundamental to this kind of incompatibility.In this paper,two aeroelastic models are presented and discussed,one of indicial-function-denoted (IF-denoted) and another of rational-function-denoted (RF-denoted).It is shown that,in cases of low wind speeds,the IF-denoted model reflects correctly the mean wind load properties,and results in correct mean structural responses;in contrast,the RF-denoted model leads to incorrect mean responses due to its nonphysical mean properties.At very high wind speeds,however,even the IF-denoted model can lead to significant deviation from the correct response due to steady aerodynamic nonlinearity.To solve the incompatibility at high wind speeds,a methodology of subtraction of pseudo-steady effects from the aeroelastic model is put forward in this work.Finally,with the method presented,aeroelastic nonlinearity resulted from the mean wind response is investigated at both moderate and high wind speeds.
基金supported by the National Key R&D Plan of China(No.2018YFB1501104)the National Natural Science Foundation of China(Grant No.52278511)+1 种基金the Natural Science Foundation of Hebei Province(No.E2021210053)the Young Backbone Teacher Cultivation Program of Henan University of Technology.
文摘Slope variation will significantly affect the characteristics of the wind field around a hill.This paper conducts a large-eddy simulation(LES)on an ideal 3D hill to study the impact of slope on wind field properties.Eight slopes ranging from 10°to 45°at 5°intervals are considered,which covers most conventional hill slopes.The inflow turbulence for the LES is generated by adopting a modified generation method that combines the equilibrium boundary conditions with the Fluent inherent vortex method to improve the simulation accuracy.The time-averaged flow field and the instantaneous vortex structure under the eight slopes are comparatively analyzed.The accuracy of the present method is verified by comparison with experimental data.The slope can affect both the mean and fluctuating wind flow fields around the 3D hill,especially on the hilltop and the leeward side,where a critical slope of 25°can be observed.The fluctuating wind speeds at the tops of steep hills(with slope angles beyond 25°)decrease with increasing slope,while the opposite phenomenon occurs on gentle hills.With increasing slope,the energy of the high-speed descending airflow is enhanced and pushes the separated flow closer to the hill surface,resulting in increased wind speed near the wall boundary on the leeward side and inhibiting the development of turbulence.The vortex shedding trajectory in the wake region becomes wider and longer,suppressing the growth of the mean wind near the wall boundary and enhancing the turbulence intensity.
基金The authors grateftilly acknowledge the support of the Ministry of Science and Technology of China(Grant Nos.2015CB452806 and 2018YFB1501104)the National Natural Science Foundation of China(Grant Nos.51408196 and 41805088)+1 种基金the Natural Science Foundation of Shanghai(Grant No.19ZR1469200)the Young Backbone Teacher Cultivation Program of Henan University of Technology.
文摘Complicated terrain was considered and simplified as two-dimensional(2D)terrain in a dynamical downscaling model and a parametric wind field model for typhoons developed by the Shanghai Typhoon Institute.The 2D terrain was further modeled as uphill and downhill segments with various slope angles relative to the incoming flow.The wind speed ratios and pressure characteristics around the 2D terrain were numerically and experimentally investigated in this study.Aerodynamic characteristics of the 2D terrain with a limitedlength upper surface were first investigated in the wind tunnel with sheared incoming flow.The corresponding numerical investigation was also conducted by using the commercial computational fluid dynamics code FLUENT with the realizable k-ε turbulence model.Special efforts were made to maintain the inflow boundary conditions throughout the computational domain.Aerodynamic characteristics were then investigated for the ideal 2D terrain with an unlimited-length upper surface by using a numerical method with uniform incoming flow.Comparisons of the different terrain models and incoming flows from the above studies show that the wind pressure coefficients and the wind speed ratios are both affected by the slope angle.A negative peak value of the wind pressure coefficients exists at the escarpment point,where flow separation occurs,for the uphill and downhill terrain models with slope angles of 40°and 30°,respectively.Correspondingly,the streamwise wind speed ratios at the points above the escarpment point for the uphill terrain model increase with increasing slope angle,reach their peak values at the slope angle of a=40°and decrease when the slope angle increases further.For the downhill terrain model,similar trends exist at the points above the escarpment point with the exception that the critical slope angle is a=30°.
基金The authors would like to gratefully acknowledge the supports from the National Natural Science Foundation of China(Grant No.50738002)and from the School of Civil Engineering and Architecture of Changsha University of Science and Technology and the Wind Engineering Research Center of Hunan University in China.
文摘Based on the spatial model,a reliable and accurate calculation method on the shape finding of self anchored suspension bridge with spatial cables was studiedin this paper.On the principle that the shape of the main cables between hangers is catenary,the iteration method of calculating the shapes of the spatial main cables under the load of hanger forces was deduced.The reasonable position of the saddle was determined according to the shape and the theoretical joint point of the main cables.The shapes of the main cables at completed cable stage werecalculated based on the unchanging principle of the zero-stress lengths of the main cables.By using a numerical method combining with the finite element method,one self-anchored suspension bridge with spatial cables was analyzed.The zero-stress length of the main cables,the position of the saddle,and the pre-offsetting of the saddle of the self-anchored suspension bridge were given.The reasonable shapes of the main cables at bridge completion stage and completed cable stage were presented.The results show that the shape-finding calculation method is effective and reliable.
文摘Flutter derivatives are essential for flutter analysis of long-span bridges,and they are generally identified from the vibration testing data of a sectional model suspended in a wind tunnel.Making use of the forced vibration testing data of three sectional models,namely,a thin-plate model,a nearly streamlined model,and a bluff-body model,a comparative study was made to identify the flutter derivatives of each model by using a time-domain method and a frequency-domain method.It was shown that all the flutter derivatives of the thin-plate model identified with the frequency-domain method and time-domain method,respectively,agree very well.Moreover,some of the flutter derivatives of each of the other two models identified with the two methods deviate to some extent.More precisely,the frequency-domain method usually results in smooth curves of the flutter derivatives.The formulation of time-domain method makes the identification results of flutter derivatives relatively sensitive to the signal phase lag between vibration state vector and aerodynamic forces and also prone to be disturbed by noise and nonlinearity.
基金The work was supported by the National Natural Science Foundation of China(Grant No.50608030).
文摘The aerodynamic interference effects on aero-static coefficients of twin deck bridges with large span were investigated in detail by means of wind tunnel test.The distances between the twin decks and wind attack angles were changed during the wind tunnel test to study the effects on aerodynamic interferences of aerostatic coefficients of twin decks.The research results have shown that the drag coefficients of the leeward deck are much smaller than that of a single leeward deck.The drag coefficients of a windward deck decrease slightly com-pared with that of a single deck.The lift and torque coefficients of windward and leeward decks are also affected slightly by the aerodynamic interference of twin decks.And the aerodynamic interference effects on lift and torque coefficients of twin decks can be neglected.
基金The authors gratefully acknowledge the coordinated support from the Natural Science Foundation of China(Grant No.5190080465)This research was also supported by the joint research project of the Wind Engineering Research Center,Tokyo Polytechnic University.(MEXT(Japan)Promotion of Distinctive Joint Research Center Program Grant Number:JPMXP0619217840,JURC grant number 20202007).
文摘An indoor thermal environment is affected by various heat elements,such as heat transfer through walls,solar radiation,and heat emissions from people,lighting and equipment.To promote both local thermal comfort and building energy efficiency,demand-oriented ventilation(such as personalized ventilation)has been developed.When using this method,a good understanding on indoor temperature distribution becomes necessary.For this purpose,an index known as Contribution Ratio of Indoor Climate(CRI)has been developed through extraction from the calculation results of Computational Fluid Dynamics(CFD).This index can be used to analyze the independent contribution of each heat element to indoor temperature distribution.In this paper,a complete and detailed introduction of the CRI is given,including its basic premises,definitions,and mathematical meaning.Particularly,calculation method of the CRI in natural convection airflow fields is further developed.Two cases(forced and natural convection airflow fields)have been carried out in different scenarios,with results showing that the CRI of a heat source had higher values in the area around itself.Also,it had a larger influence range in forced convection airflow field because of the convective airflow,while relatively larger CRI values only appear in the area above the heat source in the natural convection airflow field because of the heat plume.As a useful index for understanding the form of indoor temperature field,the CRI has guiding significance for regulating air-conditioning/ventilation systems to build better indoor thermal environment.
