Three rigid-body-motion DOFs are introduced for the motion of the flap, laghinge and pitch bearing. The rotor blade is discretized using a five-nodes, 15 DOFs beam finiteelement. The dynamic coupling effect between th...Three rigid-body-motion DOFs are introduced for the motion of the flap, laghinge and pitch bearing. The rotor blade is discretized using a five-nodes, 15 DOFs beam finiteelement. The dynamic coupling effect between the rigid motion of the blade and the nonlinear elasticdeflections is taken into account. Utilizing the constitutive law of the curvilinear coordinatesystem, the typical moderate deflection beam theory is reformulated. In addition, the Leishman andBeddoes unsteady and dynamic stall model is incorporated and the inflow is evaluated with the freewake analysis. The derived nonlinear ordinary differential equations with time - dependentcoefficients of the rotor blade are given in the sense of the generalized forces. The sectionalloads of the blade and the equations of motion are solved simultaneously in the physical space. Theblade vibratory loads predicted by present analysis show generally fair a-greement with the flighttest data of the SA349/2 Gazelle helicopter.展开更多
In this paper, the unsteady effect of airflow is introduced into the calculation of aircraft maneuver load, and the results are compared with those obtained by quasi-steady method. Taking the steep pitch maneuver of a...In this paper, the unsteady effect of airflow is introduced into the calculation of aircraft maneuver load, and the results are compared with those obtained by quasi-steady method. Taking the steep pitch maneuver of an aircraft as an example, two methods are used to calculate the aircraft response after the rudder input is given according to the specifications. The calculation results show that if the peak overload of the aircraft is the same, the horizontal tail load increases by about 1% when the unsteady effect of the airflow is taken into account. If the rudder input of the two methods is the same, the unsteady calculation method will increase more. At the same time, the calculation shows that the bigger the deflection speed of rudder surface is, the bigger the difference between them is. Therefore, in order to improve the design quality of aircraft, it is necessary to introduce the unsteady effect into the calculation of loads in the detailed design stage of aircraft.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
An unsteady load calculation method for the support configuration of a monopile-supported offshore wind turbine is developed based on the Fluent software platform.Firstly,the water wave is generated by imposing the in...An unsteady load calculation method for the support configuration of a monopile-supported offshore wind turbine is developed based on the Fluent software platform.Firstly,the water wave is generated by imposing the inlet boundary conditions according to the exact potential flow solution.Then the wave evolution is simulated by solving the unsteady incompressible Navier-Stokes(N-S)equations coupled with the volume of fluid method.For the small amplitude wave with reasonable wave parameters,the numerical wave result agrees well with that of the given wave model.Finally,a monopile support configuration is introduced and a CFD-based load calculation method is established to accurately calculate the unsteady load under the combined action of wave and wind.The computed unsteady wave load on a small-size monopile support located in the small amplitude wave flow coincides with that of the Morison formula.The load calculations are also performed on a large-size monopile support and a monopile-supported offshore wind turbine under the combined action of small amplitude wave and wind.展开更多
The research of hub vibratory loads is a very complicated problem of blade aeroelastic response. Based on the airflow environment of blade, the method of hub vibratory loads prediction will be produced when the helico...The research of hub vibratory loads is a very complicated problem of blade aeroelastic response. Based on the airflow environment of blade, the method of hub vibratory loads prediction will be produced when the helicopter flights forward with high speed. It involves the Leishman-Beddoes unsteady model and dynamic stall model, the dynamic inflow theory, the Piters-He generalized dynamic wake theory, elastic flap movement of blade and so on. The State-Space method is used to solve the equation, which is fit for numerical calculation. Comparing calculational results of several models, it is revealed that the distributions of rotor wake and blade dynamic response have great influence upon the hub vibratory loads prediction.展开更多
文摘Three rigid-body-motion DOFs are introduced for the motion of the flap, laghinge and pitch bearing. The rotor blade is discretized using a five-nodes, 15 DOFs beam finiteelement. The dynamic coupling effect between the rigid motion of the blade and the nonlinear elasticdeflections is taken into account. Utilizing the constitutive law of the curvilinear coordinatesystem, the typical moderate deflection beam theory is reformulated. In addition, the Leishman andBeddoes unsteady and dynamic stall model is incorporated and the inflow is evaluated with the freewake analysis. The derived nonlinear ordinary differential equations with time - dependentcoefficients of the rotor blade are given in the sense of the generalized forces. The sectionalloads of the blade and the equations of motion are solved simultaneously in the physical space. Theblade vibratory loads predicted by present analysis show generally fair a-greement with the flighttest data of the SA349/2 Gazelle helicopter.
文摘In this paper, the unsteady effect of airflow is introduced into the calculation of aircraft maneuver load, and the results are compared with those obtained by quasi-steady method. Taking the steep pitch maneuver of an aircraft as an example, two methods are used to calculate the aircraft response after the rudder input is given according to the specifications. The calculation results show that if the peak overload of the aircraft is the same, the horizontal tail load increases by about 1% when the unsteady effect of the airflow is taken into account. If the rudder input of the two methods is the same, the unsteady calculation method will increase more. At the same time, the calculation shows that the bigger the deflection speed of rudder surface is, the bigger the difference between them is. Therefore, in order to improve the design quality of aircraft, it is necessary to introduce the unsteady effect into the calculation of loads in the detailed design stage of aircraft.
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 partly by the National Basic Research Program of China("973"Program)(No.2014CB046200)the National Natural Science Foundation of China(No.11372135)the NUAA Fundamental Research Funds(No.NS2013005)
文摘An unsteady load calculation method for the support configuration of a monopile-supported offshore wind turbine is developed based on the Fluent software platform.Firstly,the water wave is generated by imposing the inlet boundary conditions according to the exact potential flow solution.Then the wave evolution is simulated by solving the unsteady incompressible Navier-Stokes(N-S)equations coupled with the volume of fluid method.For the small amplitude wave with reasonable wave parameters,the numerical wave result agrees well with that of the given wave model.Finally,a monopile support configuration is introduced and a CFD-based load calculation method is established to accurately calculate the unsteady load under the combined action of wave and wind.The computed unsteady wave load on a small-size monopile support located in the small amplitude wave flow coincides with that of the Morison formula.The load calculations are also performed on a large-size monopile support and a monopile-supported offshore wind turbine under the combined action of small amplitude wave and wind.
文摘The research of hub vibratory loads is a very complicated problem of blade aeroelastic response. Based on the airflow environment of blade, the method of hub vibratory loads prediction will be produced when the helicopter flights forward with high speed. It involves the Leishman-Beddoes unsteady model and dynamic stall model, the dynamic inflow theory, the Piters-He generalized dynamic wake theory, elastic flap movement of blade and so on. The State-Space method is used to solve the equation, which is fit for numerical calculation. Comparing calculational results of several models, it is revealed that the distributions of rotor wake and blade dynamic response have great influence upon the hub vibratory loads prediction.
