On the basis of the data, the source history and empirical formulas of the aerodynamic admittance function are systematically introduced. The author also briefly introduces the author's latest achievements and progress in the field of pneumatic admittance research, which provides a reference for future research work.
The forced vibration caused by turbulent wind in the atmospheric boundary layer is called chattering. Chattering is a type of limiting vibration. It occurs frequently and may cause structural fatigue. At the same time, excessive buffeting amplitude will affect the comfort and safety of use. Many structures are exposed to natural winds. Therefore, due to safety and comfort considerations, people have been asked to study the buffeting response of various structures, such as the bridges of airplanes and rafts, and the bridges of the old houses. The key to the åœ® åœ® åœ® å¼•èµ· å¼•èµ· å¼•èµ· å¼•èµ· å¼•èµ· æ¦‚å¿µ æ¦‚å¿µ æ¦‚å¿µ 1 1 1 1 1 æ¦‚å¿µ æ¦‚å¿µ æ¦‚å¿µ æ¦‚å¿µ æ¦‚å¿µ æ¦‚å¿µ æ¦‚å¿µ 1 æ¦‚å¿µ æ¦‚å¿µ æ¦‚å¿µ æ¦‚å¿µ æ¦‚å¿µ æ¦‚å¿µ æ¦‚å¿µ æ¦‚å¿µ æ¦‚å¿µ æ¦‚å¿µ æ¦‚å¿µ æ¦‚å¿µ æ¦‚å¿µ æ¦‚å¿µ æ¦‚å¿µ æ¦‚å¿µ æ¦‚å¿µ æ¦‚å¿µ æ¦‚å¿µ æ¦‚å¿µ æ¦‚å¿µTo elicit the concept of aerodynamic admittance, first look at the hDavenportllt44fdj model. For the point structure, it is empirically suggested that the aerodynamic force acting on the object is the D feature length, the mass reference area is W2M; the C0 drag coefficient, and the virtual mass coefficient includes the additional or combined mass coefficient.
The force term, the term is the inertia term associated with fluid acceleration. The first generation was very special, and it was ignored at 1 o'clock in the discussion. The wind speed is averaged by 4 superimposed pulsating winds. Ignoring the inertia term and the square term of 1 considers that the coefficient 6 of the moving part of the equation is small compared with the lower one, and it is now the change of the frequency of the mountain. Therefore, the ratio of the aerodynamic admittance coefficient to the constant aerodynamic coefficient 0 is obtained. Introduce the concept from the above. The aerodynamic admittance is to correct the unsteady power to the quasi-steady aerodynamic force. 2 The aerodynamic admittance study reviews the aerodynamic lift of the cargo section under the vertical sinusoidal pulsating wind in 1èˆ›0. The torque thus gives the wing section machine Tan. Advance speed for the vertical claw string gust to receive the date 20021028; revised date 200216 fund project home! However, the science-funded project 5,9540 is up to the class of the Searle function and the repair, and the Sel function. Then 1 button magic 2 is the so-called 3, function, this function form is very complicated, for ease of application, it has the following two approximation formulas can be seen from the above derivation, 3, the essence of the function is the vertical pulsating wind speed The lift aerodynamic admittance caused by the thin wing, and also find a constant multiple relationship between lift and torque, so the 369 function can also be used as a vertical pulsating wind speed on the thin wing to cause the wind speed to change with time. The spatial structure of the flow field is therefore applied to the corrections that need to be improved in the dimensional theory. 2.2 Study of aerodynamic admittance 221 Theoretical research and theoretical research on aerodynamic admittance, the earliest is the gas of the wing section of the 51-year-old derivation of the same sinusoidal pulsating wind The power, which is the basis of the wing section, is also given. The pulsation resistance theory of the bridge section is also of great value for the preliminary estimation of the aerodynamic admittance.
2.2.2 Experimental research Theories are limited to special sections or special cases, and the actual structure types are ever-changing. Therefore, most of the research work is carried out in the experimental field, including the aerodynamic guidance of various structural sections. The measuring plate of the nanometer, called the resistance of the prismatic raft 1217, the aerodynamic admittance of the bridge, the lift of the bridge 22 22, the movement of the dynamometer, the experimental study of the parameters affecting the aerodynamic admittance, such as the turbulent spatial correlation turbulence 317 wind speed fold; salt frequency 3122 turbulent enthalpy scale and object feature size ratio pit 142321 aspect ratio and width and thickness 2 and Reynolds number 7 and other effects on the aerodynamic admittance. The test mortar provides one-stop data for the pneumatic admittance of the structural section.
2.2.3 Pneumatic admittance test measurement The measurement of the pneumatic admittance is carried out in the wind tunnel, and the turbulent pulsating wind uses the active gust generator device to generate turbulence. Passive turbulence, 2125 girders or spires. A hot wire anemometer is used for the measurement of turbulence. Pneumatic admittance measurement test whistle 3 types of rigid body segment type 23237 aeroelastic mold 537 and brace model 267. There are roughly two types of identification methods. Identification is made by measuring system response 257. To identify by directly measuring the chatter 33. 2.3 The empirical formula of aerodynamic admittance is obtained from the 3, after the introduction of the concept of 1 motion and 3 nanometers in the buffeting analysis of long-span bridges, the 1st motion admittance is widely used in the vibration analysis of various structures. Therefore, A lot of structures, Cheng Shi have carried out a series of experimental research on aerodynamic admittance, and introduced a lot of heart formula for the lift aerodynamic admittance formula of the fire spanning suspension bridge for the pneumatic treatment of commercial buildings; Qing and Ru The milk 15 obtains the lateral resistance of the carriage and the aerodynamic admittance formula is the theoretical estimate of the force. After that, under the assumption of the strip theory, the plate grid theory is used to estimate the pulsation resistance of the bluff body structure, and the theoretical estimation of the bluff body structure resistance aerodynamic admittance is obtained. The rapid admittance of the gusts on the offshore platform, the aerodynamic admittance formula is the width and height of the hoist; 0, wind, Xie Xian factor.
It is thought that the pneumatic admittance in the various nanostructures chattering analysis is called the experience of the proposed method. They should all be filled with their own conditions and limitations and can therefore only be applied during chattering analysis of a particular structure or situation. It is undeniable that their application plays an important role in the preliminary estimation of the buffeting force.
3 questions are summarized, the literature is reviewed and divided. The research on pneumatic admittance can be summarized as follows.
1. The aerodynamic admittance function is an important aerodynamic parameter in the calculation of the buffeting response of the bridge structure. 2 The solvable solution to the aerodynamic admittance is ambiguous. There is no clear definition of the concept of aerodynamic admittance. The physical meaning of aerodynamic admittance is also not clear. The theoretical study on aerodynamic admittance is also preliminary; the test, theory and technique for measuring aerodynamic admittance are not very mature; The experience of aerodynamic admittance function suitable for engineering applications must be redefined for the concept of aerodynamic admittance, and the physical meaning of aerodynamic admittance must be clarified, and the theory of aerodynamic admittance should be improved. On this basis, the research on the experimental identification theory and technology of the pneumatic admittance can effectively identify the six aerodynamic admittance coefficients by means of the test, and finally obtain the aerodynamic admittance function suitable for engineering applications. The new progress of the research is aimed at the above research objectives. The author has studied the aerodynamic admittance with the existing research results obtained by the predecessors. Some new definitions of the aerodynamic admittance function. The aerodynamic admittance is a structural chattering analysis. The most important thing is the quantity that determines the pulsating wind (1) the setting of the juice of the structure's buffeting force. In the past, it was considered that the aerodynamic admittance is a transfer function between the connected pulsating wind and the buffeting force, or a transfer function. The standard pulsation spectrum is multiplied by the aerodynamic admittance to obtain the çœº power spectrum. However, from its source, it seems that the transfer function is not suitable. The proposal of aerodynamic admittance is firstly based on the quasi-steady theory. That is to say, the unsteady aerodynamic force should be determined by the quasi-steady aerodynamic force, so that the concept of pneumatic admittance is adopted to fix the constant aerodynamic force to the unsteady aerodynamic force.
It can be seen from this that the essence of aerodynamic admittance is only a correction coefficient to obtain the unsteady characteristics of aerodynamic force with its correction result or can define the aerodynamic admittance. It is a quasi-stationary constant aerodynamic force, and its essence reflects the unsteady gas. The change of the dynamic coefficient relative to the constant aerodynamic coefficient is used to describe the ratio of the pulsating wind speed acting on the structural force coefficient and the steady aerodynamic coefficient.
4.2 Physical Meaning of Pneumatic Admittance As can be seen from the above definition, the aerodynamic admittance function is a correction coefficient describing the aerodynamic unsteady characteristics of the pulsating attack speed on the structure, so it contains all the exemplified or pulsating aerodynamic unsteady characteristics. the elements of. There are many influencing factors for aerodynamic admittance, and all influencing factors should be included in the aerodynamic admittance function. It can be known from theoretical derivation or experimental research. The shape of the structure of the aerodynamic admittance function that depends on the decreasing frequency of the pulsating wind speed will also affect the form of the aerodynamic admittance. The aerodynamic admittance of the bluff body section and the streamline ç”© section is definitely different; the turbulent space correlation effect will affect the size of the aerodynamic admittance, so the aerodynamic admittance also reflects the influence of the turbulent space correlation effect; Influencing factors such as the aspect ratio and the aspect ratio of the turbulent turbulent integral scale structure are also not negligible.
In summary, the physical meaning of aerodynamic admittance reflects all the unsteady mechanisms of interaction between random turbulence and structure, reflecting the difference between quasi-stationary aerodynamic and unsteady aerodynamic forces.
4.3 Identification Theory of Pneumatic Admittance From the previous experimental research, the measurement methods of pneumatic admittance are various. The results are not exhaustive. This is mainly due to the fact that the measurement of the ten pneumatic admittance does not have a technical standard. Same as the pneumatic admittance. The theory is not perfect enough, and different researches have a slightly different understanding of this concept, which has led to the situation that the current calculation of the chattering force is based on the 5,313 quasi-constant and the pneumatic admittance correction. In this way, there are 6 aerodynamic admittance correction coefficients that are called to recognize the aerodynamic admittance correction coefficient of the bridge section by the scientific research worker. Nano measurement technology research is also necessary.
In view of this purpose, the author proposes a cross-power spectrum method, which is to obtain six simultaneous equations, and finally solve for six aerodynamic admittance correction coefficients. This theoretical method can simultaneously test three buffeting forces through experimental means. The time-history curve of the component and the two pulsating wind speed components, and then the cross-power spectrum. Effectively, six aerodynamic admittance correction factors were obtained.
5 Summary and Prospects As the span of bridges increases, important factors are caused by atmospheric turbulence. Therefore, the research on bridge buffeting response has become an important research and content of bridge engineers, and the aerodynamic admittance correction coefficient is the claw vertical aerodynamic parameter in the buffeting response analysis. Therefore, the research on aerodynamic admittance has a strong engineering practical significance.
The research has redefine the concept of aerodynamic admittance, clarifies the physical meaning of aerodynamic admittance, and proposes a recognition theory cross-power spectrum method that effectively identifies six aerodynamic admittance correction coefficients, but due to the diversity of bridge sections And the complexity of the factors affecting the aerodynamic admittance, it is difficult to derive the theoretical aerodynamic admittance. Although the predecessors have obtained experimental formulas through experimental or theoretical estimation, the application of these formulas is only suitable for specific occasions or structures, and the application range is limited. The current chattering calculation considers the aerodynamic admittance to be very rough. It is considered as two or three functions. In view of this situation, the goal of the research is to propose the cross-power spectrum method. Based on the recognition theory, the wind tunnel test is used to measure the aerodynamic admittance correction coefficient of a series of typical bridge sections, so as to fit the empirical formula of aerodynamic admittance that can meet the engineering requirements, thus providing the first step for the refinement of bridge buffeting analysis. Hand information.
Jiang Yonglin. Analysis of buffeting response of cable-stayed bridges. 0. Chengdu Southwest Jiaotong University, 2000.
Responsible editor Yuan Benkui
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